diff options
| -rw-r--r-- | Documentation/RCU/trace.txt | 144 | ||||
| -rw-r--r-- | include/linux/init_task.h | 9 | ||||
| -rw-r--r-- | include/linux/rculist.h | 5 | ||||
| -rw-r--r-- | include/linux/rcupdate.h | 4 | ||||
| -rw-r--r-- | include/linux/rcutiny.h | 13 | ||||
| -rw-r--r-- | include/linux/rcutree.h | 2 | ||||
| -rw-r--r-- | include/linux/sched.h | 11 | ||||
| -rw-r--r-- | init/Kconfig | 55 | ||||
| -rw-r--r-- | kernel/rcutiny.c | 105 | ||||
| -rw-r--r-- | kernel/rcutiny_plugin.h | 433 | ||||
| -rw-r--r-- | kernel/rcutorture.c | 270 | ||||
| -rw-r--r-- | kernel/rcutree.c | 156 | ||||
| -rw-r--r-- | kernel/rcutree.h | 61 | ||||
| -rw-r--r-- | kernel/rcutree_plugin.h | 135 | ||||
| -rw-r--r-- | kernel/rcutree_trace.c | 12 | ||||
| -rw-r--r-- | kernel/sched.c | 69 | ||||
| -rw-r--r-- | kernel/srcu.c | 8 |
17 files changed, 1207 insertions, 285 deletions
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt index a851118775d8..6a8c73f55b80 100644 --- a/Documentation/RCU/trace.txt +++ b/Documentation/RCU/trace.txt @@ -1,18 +1,22 @@ CONFIG_RCU_TRACE debugfs Files and Formats -The rcutree implementation of RCU provides debugfs trace output that -summarizes counters and state. This information is useful for debugging -RCU itself, and can sometimes also help to debug abuses of RCU. -The following sections describe the debugfs files and formats. +The rcutree and rcutiny implementations of RCU provide debugfs trace +output that summarizes counters and state. This information is useful for +debugging RCU itself, and can sometimes also help to debug abuses of RCU. +The following sections describe the debugfs files and formats, first +for rcutree and next for rcutiny. -Hierarchical RCU debugfs Files and Formats +CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats -This implementation of RCU provides three debugfs files under the +These implementations of RCU provides five debugfs files under the top-level directory RCU: rcu/rcudata (which displays fields in struct -rcu_data), rcu/rcugp (which displays grace-period counters), and -rcu/rcuhier (which displays the struct rcu_node hierarchy). +rcu_data), rcu/rcudata.csv (which is a .csv spreadsheet version of +rcu/rcudata), rcu/rcugp (which displays grace-period counters), +rcu/rcuhier (which displays the struct rcu_node hierarchy), and +rcu/rcu_pending (which displays counts of the reasons that the +rcu_pending() function decided that there was core RCU work to do). The output of "cat rcu/rcudata" looks as follows: @@ -130,7 +134,8 @@ o "ci" is the number of RCU callbacks that have been invoked for been registered in absence of CPU-hotplug activity. o "co" is the number of RCU callbacks that have been orphaned due to - this CPU going offline. + this CPU going offline. These orphaned callbacks have been moved + to an arbitrarily chosen online CPU. o "ca" is the number of RCU callbacks that have been adopted due to other CPUs going offline. Note that ci+co-ca+ql is the number of @@ -168,12 +173,12 @@ o "gpnum" is the number of grace periods that have started. It is The output of "cat rcu/rcuhier" looks as follows, with very long lines: -c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6 oqlen=0 +c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6 1/1 .>. 0:127 ^0 3/3 .>. 0:35 ^0 0/0 .>. 36:71 ^1 0/0 .>. 72:107 ^2 0/0 .>. 108:127 ^3 3/3f .>. 0:5 ^0 2/3 .>. 6:11 ^1 0/0 .>. 12:17 ^2 0/0 .>. 18:23 ^3 0/0 .>. 24:29 ^4 0/0 .>. 30:35 ^5 0/0 .>. 36:41 ^0 0/0 .>. 42:47 ^1 0/0 .>. 48:53 ^2 0/0 .>. 54:59 ^3 0/0 .>. 60:65 ^4 0/0 .>. 66:71 ^5 0/0 .>. 72:77 ^0 0/0 .>. 78:83 ^1 0/0 .>. 84:89 ^2 0/0 .>. 90:95 ^3 0/0 .>. 96:101 ^4 0/0 .>. 102:107 ^5 0/0 .>. 108:113 ^0 0/0 .>. 114:119 ^1 0/0 .>. 120:125 ^2 0/0 .>. 126:127 ^3 rcu_bh: -c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0 oqlen=0 +c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0 0/1 .>. 0:127 ^0 0/3 .>. 0:35 ^0 0/0 .>. 36:71 ^1 0/0 .>. 72:107 ^2 0/0 .>. 108:127 ^3 0/3f .>. 0:5 ^0 0/3 .>. 6:11 ^1 0/0 .>. 12:17 ^2 0/0 .>. 18:23 ^3 0/0 .>. 24:29 ^4 0/0 .>. 30:35 ^5 0/0 .>. 36:41 ^0 0/0 .>. 42:47 ^1 0/0 .>. 48:53 ^2 0/0 .>. 54:59 ^3 0/0 .>. 60:65 ^4 0/0 .>. 66:71 ^5 0/0 .>. 72:77 ^0 0/0 .>. 78:83 ^1 0/0 .>. 84:89 ^2 0/0 .>. 90:95 ^3 0/0 .>. 96:101 ^4 0/0 .>. 102:107 ^5 0/0 .>. 108:113 ^0 0/0 .>. 114:119 ^1 0/0 .>. 120:125 ^2 0/0 .>. 126:127 ^3 @@ -212,11 +217,6 @@ o "fqlh" is the number of calls to force_quiescent_state() that exited immediately (without even being counted in nfqs above) due to contention on ->fqslock. -o "oqlen" is the number of callbacks on the "orphan" callback - list. RCU callbacks are placed on this list by CPUs going - offline, and are "adopted" either by the CPU helping the outgoing - CPU or by the next rcu_barrier*() call, whichever comes first. - o Each element of the form "1/1 0:127 ^0" represents one struct rcu_node. Each line represents one level of the hierarchy, from root to leaves. It is best to think of the rcu_data structures @@ -326,3 +326,115 @@ o "nn" is the number of times that this CPU needed nothing. Alert readers will note that the rcu "nn" number for a given CPU very closely matches the rcu_bh "np" number for that same CPU. This is due to short-circuit evaluation in rcu_pending(). + + +CONFIG_TINY_RCU and CONFIG_TINY_PREEMPT_RCU debugfs Files and Formats + +These implementations of RCU provides a single debugfs file under the +top-level directory RCU, namely rcu/rcudata, which displays fields in +rcu_bh_ctrlblk, rcu_sched_ctrlblk and, for CONFIG_TINY_PREEMPT_RCU, +rcu_preempt_ctrlblk. + +The output of "cat rcu/rcudata" is as follows: + +rcu_preempt: qlen=24 gp=1097669 g197/p197/c197 tasks=... + ttb=. btg=no ntb=184 neb=0 nnb=183 j=01f7 bt=0274 + normal balk: nt=1097669 gt=0 bt=371 b=0 ny=25073378 nos=0 + exp balk: bt=0 nos=0 +rcu_sched: qlen: 0 +rcu_bh: qlen: 0 + +This is split into rcu_preempt, rcu_sched, and rcu_bh sections, with the +rcu_preempt section appearing only in CONFIG_TINY_PREEMPT_RCU builds. +The last three lines of the rcu_preempt section appear only in +CONFIG_RCU_BOOST kernel builds. The fields are as follows: + +o "qlen" is the number of RCU callbacks currently waiting either + for an RCU grace period or waiting to be invoked. This is the + only field present for rcu_sched and rcu_bh, due to the + short-circuiting of grace period in those two cases. + +o "gp" is the number of grace periods that have completed. + +o "g197/p197/c197" displays the grace-period state, with the + "g" number being the number of grace periods that have started + (mod 256), the "p" number being the number of grace periods + that the CPU has responded to (also mod 256), and the "c" + number being the number of grace periods that have completed + (once again mode 256). + + Why have both "gp" and "g"? Because the data flowing into + "gp" is only present in a CONFIG_RCU_TRACE kernel. + +o "tasks" is a set of bits. The first bit is "T" if there are + currently tasks that have recently blocked within an RCU + read-side critical section, the second bit is "N" if any of the + aforementioned tasks are blocking the current RCU grace period, + and the third bit is "E" if any of the aforementioned tasks are + blocking the current expedited grace period. Each bit is "." + if the corresponding condition does not hold. + +o "ttb" is a single bit. It is "B" if any of the blocked tasks + need to be priority boosted and "." otherwise. + +o "btg" indicates whether boosting has been carried out during + the current grace period, with "exp" indicating that boosting + is in progress for an expedited grace period, "no" indicating + that boosting has not yet started for a normal grace period, + "begun" indicating that boosting has bebug for a normal grace + period, and "done" indicating that boosting has completed for + a normal grace period. + +o "ntb" is the total number of tasks subjected to RCU priority boosting + periods since boot. + +o "neb" is the number of expedited grace periods that have had + to resort to RCU priority boosting since boot. + +o "nnb" is the number of normal grace periods that have had + to resort to RCU priority boosting since boot. + +o "j" is the low-order 12 bits of the jiffies counter in hexadecimal. + +o "bt" is the low-order 12 bits of the value that the jiffies counter + will have at the next time that boosting is scheduled to begin. + +o In the line beginning with "normal balk", the fields are as follows: + + o "nt" is the number of times that the system balked from + boosting because there were no blocked tasks to boost. + Note that the system will balk from boosting even if the + grace period is overdue when the currently running task + is looping within an RCU read-side critical section. + There is no point in boosting in this case, because + boosting a running task won't make it run any faster. + + o "gt" is the number of times that the system balked + from boosting because, although there were blocked tasks, + none of them were preventing the current grace period + from completing. + + o "bt" is the number of times that the system balked + from boosting because boosting was already in progress. + + o "b" is the number of times that the system balked from + boosting because boosting had already completed for + the grace period in question. + + o "ny" is the number of times that the system balked from + boosting because it was not yet time to start boosting + the grace period in question. + + o "nos" is the number of times that the system balked from + boosting for inexplicable ("not otherwise specified") + reasons. This can actually happen due to races involving + increments of the jiffies counter. + +o In the line beginning with "exp balk", the fields are as follows: + + o "bt" is the number of times that the system balked from + boosting because there were no blocked tasks to boost. + + o "nos" is the number of times that the system balked from + boosting for inexplicable ("not otherwise specified") + reasons. diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 1f8c06ce0fa6..6b281fae114a 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -83,6 +83,12 @@ extern struct group_info init_groups; */ # define CAP_INIT_BSET CAP_FULL_SET +#ifdef CONFIG_RCU_BOOST +#define INIT_TASK_RCU_BOOST() \ + .rcu_boost_mutex = NULL, +#else +#define INIT_TASK_RCU_BOOST() +#endif #ifdef CONFIG_TREE_PREEMPT_RCU #define INIT_TASK_RCU_TREE_PREEMPT() \ .rcu_blocked_node = NULL, @@ -94,7 +100,8 @@ extern struct group_info init_groups; .rcu_read_lock_nesting = 0, \ .rcu_read_unlock_special = 0, \ .rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), \ - INIT_TASK_RCU_TREE_PREEMPT() + INIT_TASK_RCU_TREE_PREEMPT() \ + INIT_TASK_RCU_BOOST() #else #define INIT_TASK_RCU_PREEMPT(tsk) #endif diff --git a/include/linux/rculist.h b/include/linux/rculist.h index f31ef61f1c65..2dea94fc4402 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -241,11 +241,6 @@ static inline void list_splice_init_rcu(struct list_head *list, #define list_first_entry_rcu(ptr, type, member) \ list_entry_rcu((ptr)->next, type, member) -#define __list_for_each_rcu(pos, head) \ - for (pos = rcu_dereference_raw(list_next_rcu(head)); \ - pos != (head); \ - pos = rcu_dereference_raw(list_next_rcu((pos))) - /** * list_for_each_entry_rcu - iterate over rcu list of given type * @pos: the type * to use as a loop cursor. diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 03cda7bed985..af5614856285 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -47,6 +47,8 @@ extern int rcutorture_runnable; /* for sysctl */ #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ +#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) +#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) @@ -66,7 +68,6 @@ extern void call_rcu_sched(struct rcu_head *head, extern void synchronize_sched(void); extern void rcu_barrier_bh(void); extern void rcu_barrier_sched(void); -extern void synchronize_sched_expedited(void); extern int sched_expedited_torture_stats(char *page); static inline void __rcu_read_lock_bh(void) @@ -118,7 +119,6 @@ static inline int rcu_preempt_depth(void) #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ /* Internal to kernel */ -extern void rcu_init(void); extern void rcu_sched_qs(int cpu); extern void rcu_bh_qs(int cpu); extern void rcu_check_callbacks(int cpu, int user); diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 13877cb93a60..30ebd7c8d874 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -27,7 +27,9 @@ #include <linux/cache.h> -#define rcu_init_sched() do { } while (0) +static inline void rcu_init(void) +{ +} #ifdef CONFIG_TINY_RCU @@ -58,6 +60,11 @@ static inline void synchronize_rcu_bh_expedited(void) synchronize_sched(); } +static inline void synchronize_sched_expedited(void) +{ + synchronize_sched(); +} + #ifdef CONFIG_TINY_RCU static inline void rcu_preempt_note_context_switch(void) @@ -125,16 +132,12 @@ static inline void rcu_cpu_stall_reset(void) } #ifdef CONFIG_DEBUG_LOCK_ALLOC - extern int rcu_scheduler_active __read_mostly; extern void rcu_scheduler_starting(void); - #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ - static inline void rcu_scheduler_starting(void) { } - #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ #endif /* __LINUX_RCUTINY_H */ diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 95518e628794..3a933482734a 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -30,6 +30,7 @@ #ifndef __LINUX_RCUTREE_H #define __LINUX_RCUTREE_H +extern void rcu_init(void); extern void rcu_note_context_switch(int cpu); extern int rcu_needs_cpu(int cpu); extern void rcu_cpu_stall_reset(void); @@ -47,6 +48,7 @@ static inline void exit_rcu(void) #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ extern void synchronize_rcu_bh(void); +extern void synchronize_sched_expedited(void); extern void synchronize_rcu_expedited(void); static inline void synchronize_rcu_bh_expedited(void) diff --git a/include/linux/sched.h b/include/linux/sched.h index 223874538b33..d8005503cc62 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1229,6 +1229,9 @@ struct task_struct { #ifdef CONFIG_TREE_PREEMPT_RCU struct rcu_node *rcu_blocked_node; #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ +#ifdef CONFIG_RCU_BOOST + struct rt_mutex *rcu_boost_mutex; +#endif /* #ifdef CONFIG_RCU_BOOST */ #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT) struct sched_info sched_info; @@ -1759,7 +1762,8 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t * #ifdef CONFIG_PREEMPT_RCU #define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */ -#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */ +#define RCU_READ_UNLOCK_BOOSTED (1 << 1) /* boosted while in RCU read-side. */ +#define RCU_READ_UNLOCK_NEED_QS (1 << 2) /* RCU core needs CPU response. */ static inline void rcu_copy_process(struct task_struct *p) { @@ -1767,7 +1771,10 @@ static inline void rcu_copy_process(struct task_struct *p) p->rcu_read_unlock_special = 0; #ifdef CONFIG_TREE_PREEMPT_RCU p->rcu_blocked_node = NULL; -#endif +#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ +#ifdef CONFIG_RCU_BOOST + p->rcu_boost_mutex = NULL; +#endif /* #ifdef CONFIG_RCU_BOOST */ INIT_LIST_HEAD(&p->rcu_node_entry); } diff --git a/init/Kconfig b/init/Kconfig index c9728992a776..526ec1c7456a 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -393,7 +393,6 @@ config PREEMPT_RCU config RCU_TRACE bool "Enable tracing for RCU" - depends on TREE_RCU || TREE_PREEMPT_RCU help This option provides tracing in RCU which presents stats in debugfs for debugging RCU implementation. @@ -459,6 +458,60 @@ config TREE_RCU_TRACE TREE_PREEMPT_RCU implementations, permitting Makefile to trivially select kernel/rcutree_trace.c. +config RCU_BOOST + bool "Enable RCU priority boosting" + depends on RT_MUTEXES && TINY_PREEMPT_RCU + default n + help + This option boosts the priority of preempted RCU readers that + block the current preemptible RCU grace period for too long. + This option also prevents heavy loads from blocking RCU + callback invocation for all flavors of RCU. + + Say Y here if you are working with real-time apps or heavy loads + Say N here if you are unsure. + +config RCU_BOOST_PRIO + int "Real-time priority to boost RCU readers to" + range 1 99 + depends on RCU_BOOST + default 1 + help + This option specifies the real-time priority to which preempted + RCU readers are to be boosted. If you are working with CPU-bound + real-time applications, you should specify a priority higher then + the highest-priority CPU-bound application. + + Specify the real-time priority, or take the default if unsure. + +config RCU_BOOST_DELAY + int "Milliseconds to delay boosting after RCU grace-period start" + range 0 3000 + depends on RCU_BOOST + default 500 + help + This option specifies the time to wait after the beginning of + a given grace period before priority-boosting preempted RCU + readers blocking that grace period. Note that any RCU reader + blocking an expedited RCU grace period is boosted immediately. + + Accept the default if unsure. + +config SRCU_SYNCHRONIZE_DELAY + int "Microseconds to delay before waiting for readers" + range 0 20 + default 10 + help + This option controls how long SRCU delays before entering its + loop waiting on SRCU readers. The purpose of this loop is + to avoid the unconditional context-switch penalty that would + otherwise be incurred if there was an active SRCU reader, + in a manner similar to adaptive locking schemes. This should + be set to be a bit longer than the common-case SRCU read-side + critical-section overhead. + + Accept the default if unsure. + endmenu # "RCU Subsystem" config IKCONFIG diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index d806735342ac..034493724749 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -36,31 +36,16 @@ #include <linux/time.h> #include <linux/cpu.h> -/* Global control variables for rcupdate callback mechanism. */ -struct rcu_ctrlblk { - struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ - struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ - struct rcu_head **curtail; /* ->next pointer of last CB. */ -}; - -/* Definition for rcupdate control block. */ -static struct rcu_ctrlblk rcu_sched_ctrlblk = { - .donetail = &rcu_sched_ctrlblk.rcucblist, - .curtail = &rcu_sched_ctrlblk.rcucblist, -}; - -static struct rcu_ctrlblk rcu_bh_ctrlblk = { - .donetail = &rcu_bh_ctrlblk.rcucblist, - .curtail = &rcu_bh_ctrlblk.rcucblist, -}; - -#ifdef CONFIG_DEBUG_LOCK_ALLOC -int rcu_scheduler_active __read_mostly; -EXPORT_SYMBOL_GPL(rcu_scheduler_active); -#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ +/* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */ +static struct task_struct *rcu_kthread_task; +static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq); +static unsigned long have_rcu_kthread_work; +static void invoke_rcu_kthread(void); /* Forward declarations for rcutiny_plugin.h. */ -static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp); +struct rcu_ctrlblk; +static void rcu_process_callbacks(struct rcu_ctrlblk *rcp); +static int rcu_kthread(void *arg); static void __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), struct rcu_ctrlblk *rcp); @@ -123,7 +108,7 @@ void rcu_sched_qs(int cpu) { if (rcu_qsctr_help(&rcu_sched_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk)) - raise_softirq(RCU_SOFTIRQ); + invoke_rcu_kthread(); } /* @@ -132,7 +117,7 @@ void rcu_sched_qs(int cpu) void rcu_bh_qs(int cpu) { if (rcu_qsctr_help(&rcu_bh_ctrlblk)) - raise_softirq(RCU_SOFTIRQ); + invoke_rcu_kthread(); } /* @@ -152,13 +137,14 @@ void rcu_check_callbacks(int cpu, int user) } /* - * Helper function for rcu_process_callbacks() that operates on the - * specified rcu_ctrlkblk structure. + * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure + * whose grace period has elapsed. */ -static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) +static void rcu_process_callbacks(struct rcu_ctrlblk *rcp) { struct rcu_head *next, *list; unsigned long flags; + RCU_TRACE(int cb_count = 0); /* If no RCU callbacks ready to invoke, just return. */ if (&rcp->rcucblist == rcp->donetail) @@ -180,19 +166,58 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) next = list->next; prefetch(next); debug_rcu_head_unqueue(list); + local_bh_disable(); list->func(list); + local_bh_enable(); list = next; + RCU_TRACE(cb_count++); } + RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); } /* - * Invoke any callbacks whose grace period has completed. + * This kthread invokes RCU callbacks whose grace periods have + * elapsed. It is awakened as needed, and takes the place of the + * RCU_SOFTIRQ that was used previously for this purpose. + * This is a kthread, but it is never stopped, at least not until + * the system goes down. */ -static void rcu_process_callbacks(struct softirq_action *unused) +static int rcu_kthread(void *arg) { - __rcu_process_callbacks(&rcu_sched_ctrlblk); - __rcu_process_callbacks(&rcu_bh_ctrlblk); - rcu_preempt_process_callbacks(); + unsigned long work; + unsigned long morework; + unsigned long flags; + + for (;;) { + wait_event(rcu_kthread_wq, have_rcu_kthread_work != 0); + morework = rcu_boost(); + local_irq_save(flags); + work = have_rcu_kthread_work; + have_rcu_kthread_work = morework; + local_irq_restore(flags); + if (work) { + rcu_process_callbacks(&rcu_sched_ctrlblk); + rcu_process_callbacks(&rcu_bh_ctrlblk); + rcu_preempt_process_callbacks(); + } + schedule_timeout_interruptible(1); /* Leave CPU for others. */ + } + + return 0; /* Not reached, but needed to shut gcc up. */ +} + +/* + * Wake up rcu_kthread() to process callbacks now eligible for invocation + * or to boost readers. + */ +static void invoke_rcu_kthread(void) +{ + unsigned long flags; + + local_irq_save(flags); + have_rcu_kthread_work = 1; + wake_up(&rcu_kthread_wq); + local_irq_restore(flags); } /* @@ -230,6 +255,7 @@ static void __call_rcu(struct rcu_head *head, local_irq_save(flags); *rcp->curtail = head; rcp->curtail = &head->next; + RCU_TRACE(rcp->qlen++); local_irq_restore(flags); } @@ -282,7 +308,16 @@ void rcu_barrier_sched(void) } EXPORT_SYMBOL_GPL(rcu_barrier_sched); -void __init rcu_init(void) +/* + * Spawn the kthread that invokes RCU callbacks. + */ +static int __init rcu_spawn_kthreads(void) { - open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); + struct sched_param sp; + + rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread"); + sp.sched_priority = RCU_BOOST_PRIO; + sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp); + return 0; } +early_initcall(rcu_spawn_kthreads); diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 6ceca4f745ff..015abaea962a 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -22,6 +22,40 @@ * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> */ +#include <linux/kthread.h> +#include <linux/debugfs.h> +#include <linux/seq_file.h> + +#ifdef CONFIG_RCU_TRACE +#define RCU_TRACE(stmt) stmt +#else /* #ifdef CONFIG_RCU_TRACE */ +#define RCU_TRACE(stmt) +#endif /* #else #ifdef CONFIG_RCU_TRACE */ + +/* Global control variables for rcupdate callback mechanism. */ +struct rcu_ctrlblk { + struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ + struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ + struct rcu_head **curtail; /* ->next pointer of last CB. */ + RCU_TRACE(long qlen); /* Number of pending CBs. */ +}; + +/* Definition for rcupdate control block. */ +static struct rcu_ctrlblk rcu_sched_ctrlblk = { + .donetail = &rcu_sched_ctrlblk.rcucblist, + .curtail = &rcu_sched_ctrlblk.rcucblist, +}; + +static struct rcu_ctrlblk rcu_bh_ctrlblk = { + .donetail = &rcu_bh_ctrlblk.rcucblist, + .curtail = &rcu_bh_ctrlblk.rcucblist, +}; + +#ifdef CONFIG_DEBUG_LOCK_ALLOC +int rcu_scheduler_active __read_mostly; +EXPORT_SYMBOL_GPL(rcu_scheduler_active); +#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ + #ifdef CONFIG_TINY_PREEMPT_RCU #include <linux/delay.h> @@ -46,17 +80,45 @@ struct rcu_preempt_ctrlblk { struct list_head *gp_tasks; /* Pointer to the first task blocking the */ /* current grace period, or NULL if there */ - /* is not such task. */ + /* is no such task. */ struct list_head *exp_tasks; /* Pointer to first task blocking the */ /* current expedited grace period, or NULL */ /* if there is no such task. If there */ /* is no current expedited grace period, */ /* then there cannot be any such task. */ +#ifdef CONFIG_RCU_BOOST + struct list_head *boost_tasks; + /* Pointer to first task that needs to be */ + /* priority-boosted, or NULL if no priority */ + /* boosting is needed. If there is no */ + /* current or expedited grace period, there */ + /* can be no such task. */ +#endif /* #ifdef CONFIG_RCU_BOOST */ u8 gpnum; /* Current grace period. */ u8 gpcpu; /* Last grace period blocked by the CPU. */ u8 completed; /* Last grace period completed. */ /* If all three are equal, RCU is idle. */ +#ifdef CONFIG_RCU_BOOST + s8 boosted_this_gp; /* Has boosting already happened? */ + unsigned long boost_time; /* When to start boosting (jiffies) */ +#endif /* #ifdef CONFIG_RCU_BOOST */ +#ifdef CONFIG_RCU_TRACE + unsigned long n_grace_periods; +#ifdef CONFIG_RCU_BOOST + unsigned long n_tasks_boosted; + unsigned long n_exp_boosts; + unsigned long n_normal_boosts; + unsigned long n_normal_balk_blkd_tasks; + unsigned long n_normal_balk_gp_tasks; + unsigned long n_normal_balk_boost_tasks; + unsigned long n_normal_balk_boosted; + unsigned long n_normal_balk_notyet; + unsigned long n_normal_balk_nos; + unsigned long n_exp_balk_blkd_tasks; + unsigned long n_exp_balk_nos; +#endif /* #ifdef CONFIG_RCU_BOOST */ +#endif /* #ifdef CONFIG_RCU_TRACE */ }; static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { @@ -122,6 +184,210 @@ static int rcu_preempt_gp_in_progress(void) } /* + * Advance a ->blkd_tasks-list pointer to the next entry, instead + * returning NULL if at the end of the list. + */ +static struct list_head *rcu_next_node_entry(struct task_struct *t) +{ + struct list_head *np; + + np = t->rcu_node_entry.next; + if (np == &rcu_preempt_ctrlblk.blkd_tasks) + np = NULL; + return np; +} + +#ifdef CONFIG_RCU_TRACE + +#ifdef CONFIG_RCU_BOOST +static void rcu_initiate_boost_trace(void); +static void rcu_initiate_exp_boost_trace(void); +#endif /* #ifdef CONFIG_RCU_BOOST */ + +/* + * Dump additional statistice for TINY_PREEMPT_RCU. + */ +static void show_tiny_preempt_stats(struct seq_file *m) +{ + seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n", + rcu_preempt_ctrlblk.rcb.qlen, + rcu_preempt_ctrlblk.n_grace_periods, + rcu_preempt_ctrlblk.gpnum, + rcu_preempt_ctrlblk.gpcpu, + rcu_preempt_ctrlblk.completed, + "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)], + "N."[!rcu_preempt_ctrlblk.gp_tasks], + "E."[!rcu_preempt_ctrlblk.exp_tasks]); +#ifdef CONFIG_RCU_BOOST + seq_printf(m, " ttb=%c btg=", + "B."[!rcu_preempt_ctrlblk.boost_tasks]); + switch (rcu_preempt_ctrlblk.boosted_this_gp) { + case -1: + seq_puts(m, "exp"); + break; + case 0: + seq_puts(m, "no"); + break; + case 1: + seq_puts(m, "begun"); + break; + case 2: + seq_puts(m, "done"); + break; + default: + seq_printf(m, "?%d?", rcu_preempt_ctrlblk.boosted_this_gp); + } + seq_printf(m, " ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n", + rcu_preempt_ctrlblk.n_tasks_boosted, + rcu_preempt_ctrlblk.n_exp_boosts, + rcu_preempt_ctrlblk.n_normal_boosts, + (int)(jiffies & 0xffff), + (int)(rcu_preempt_ctrlblk.boost_time & 0xffff)); + seq_printf(m, " %s: nt=%lu gt=%lu bt=%lu b=%lu ny=%lu nos=%lu\n", + "normal balk", + rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks, + rcu_preempt_ctrlblk.n_normal_balk_gp_tasks, + rcu_preempt_ctrlblk.n_normal_balk_boost_tasks, + rcu_preempt_ctrlblk.n_normal_balk_boosted, + rcu_preempt_ctrlblk.n_normal_balk_notyet, + rcu_preempt_ctrlblk.n_normal_balk_nos); + seq_printf(m, " exp balk: bt=%lu nos=%lu\n", + rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks, + rcu_preempt_ctrlblk.n_exp_balk_nos); +#endif /* #ifdef CONFIG_RCU_BOOST */ +} + +#endif /* #ifdef CONFIG_RCU_TRACE */ + +#ifdef CONFIG_RCU_BOOST + +#include "rtmutex_common.h" + +/* + * Carry out RCU priority boosting on the task indicated by ->boost_tasks, + * and advance ->boost_tasks to the next task in the ->blkd_tasks list. + */ +static int rcu_boost(void) +{ + unsigned long flags; + struct rt_mutex mtx; + struct list_head *np; + struct task_struct *t; + + if (rcu_preempt_ctrlblk.boost_tasks == NULL) + return 0; /* Nothing to boost. */ + raw_local_irq_save(flags); + rcu_preempt_ctrlblk.boosted_this_gp++; + t = container_of(rcu_preempt_ctrlblk.boost_tasks, struct task_struct, + rcu_node_entry); + np = rcu_next_node_entry(t); + rt_mutex_init_proxy_locked(&mtx, t); + t->rcu_boost_mutex = &mtx; + t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; + raw_local_irq_restore(flags); + rt_mutex_lock(&mtx); + RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++); + rcu_preempt_ctrlblk.boosted_this_gp++; + rt_mutex_unlock(&mtx); + return rcu_preempt_ctrlblk.boost_tasks != NULL; +} + +/* + * Check to see if it is now time to start boosting RCU readers blocking + * the current grace period, and, if so, tell the rcu_kthread_task to + * start boosting them. If there is an expedited boost in progress, + * we wait for it to complete. + * + * If there are no blocked readers blocking the current grace period, + * return 0 to let the caller know, otherwise return 1. Note that this + * return value is independent of whether or not boosting was done. + */ +static int rcu_initiate_boost(void) +{ + if (!rcu_preempt_blocked_readers_cgp()) { + RCU_TRACE(rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks++); + return 0; + } + if (rcu_preempt_ctrlblk.gp_tasks != NULL && + rcu_preempt_ctrlblk.boost_tasks == NULL && + rcu_preempt_ctrlblk.boosted_this_gp == 0 && + ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) { + rcu_preempt_ctrlblk.boost_tasks = rcu_preempt_ctrlblk.gp_tasks; + invoke_rcu_kthread(); + RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++); + } else + RCU_TRACE(rcu_initiate_boost_trace()); + return 1; +} + +/* + * Initiate boosting for an expedited grace period. + */ +static void rcu_initiate_expedited_boost(void) +{ + unsigned long flags; + + raw_local_irq_save(flags); + if (!list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) { + rcu_preempt_ctrlblk.boost_tasks = + rcu_preempt_ctrlblk.blkd_tasks.next; + rcu_preempt_ctrlblk.boosted_this_gp = -1; + invoke_rcu_kthread(); + RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++); + } else + RCU_TRACE(rcu_initiate_exp_boost_trace()); + raw_local_irq_restore(flags); +} + +#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000); + +/* + * Do priority-boost accounting for the start of a new grace period. + */ +static void rcu_preempt_boost_start_gp(void) +{ + rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; + if (rcu_preempt_ctrlblk.boosted_this_gp > 0) + rcu_preempt_ctrlblk.boosted_this_gp = 0; +} + +#else /* #ifdef CONFIG_RCU_BOOST */ + +/* + * If there is no RCU priority boosting, we don't boost. + */ +static int rcu_boost(void) +{ + return 0; +} + +/* + * If there is no RCU priority boosting, we don't initiate boosting, + * but we do indicate whether there are blocked readers blocking the + * current grace period. + */ +static int rcu_initiate_boost(void) +{ + return rcu_preempt_blocked_readers_cgp(); +} + +/* + * If there is no RCU priority boosting, we don't initiate expedited boosting. + */ +static void rcu_initiate_expedited_boost(void) +{ +} + +/* + * If there is no RCU priority boosting, nothing to do at grace-period start. + */ +static void rcu_preempt_boost_start_gp(void) +{ +} + +#endif /* else #ifdef CONFIG_RCU_BOOST */ + +/* * Record a preemptible-RCU quiescent state for the specified CPU. Note * that this just means that the task currently running on the CPU is * in a quiescent state. There might be any number of tasks blocked @@ -148,11 +414,14 @@ static void rcu_preempt_cpu_qs(void) rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum; current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; + /* If there is no GP then there is nothing more to do. */ + if (!rcu_preempt_gp_in_progress()) + return; /* - * If there is no GP, or if blocked readers are still blocking GP, - * then there is nothing more to do. + * Check up on boosting. If there are no readers blocking the + * current grace period, leave. */ - if (!rcu_preempt_gp_in_progress() || rcu_preempt_blocked_readers_cgp()) + if (rcu_initiate_boost()) return; /* Advance callbacks. */ @@ -164,9 +433,9 @@ static void rcu_preempt_cpu_qs(void) if (!rcu_preempt_blocked_readers_any()) rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail; - /* If there are done callbacks, make RCU_SOFTIRQ process them. */ + /* If there are done callbacks, cause them to be invoked. */ if (*rcu_preempt_ctrlblk.rcb.donetail != NULL) - raise_softirq(RCU_SOFTIRQ); + invoke_rcu_kthread(); } /* @@ -178,12 +447,16 @@ static void rcu_preempt_start_gp(void) /* Official start of GP. */ rcu_preempt_ctrlblk.gpnum++; + RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++); /* Any blocked RCU readers block new GP. */ if (rcu_preempt_blocked_readers_any()) rcu_preempt_ctrlblk.gp_tasks = rcu_preempt_ctrlblk.blkd_tasks.next; + /* Set up for RCU priority boosting. */ + rcu_preempt_boost_start_gp(); + /* If there is no running reader, CPU is done with GP. */ if (!rcu_preempt_running_reader()) rcu_preempt_cpu_qs(); @@ -304,14 +577,16 @@ static void rcu_read_unlock_special(struct task_struct *t) */ empty = !rcu_preempt_blocked_readers_cgp(); empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL; - np = t->rcu_node_entry.next; - if (np == &rcu_preempt_ctrlblk.blkd_tasks) - np = NULL; + np = rcu_next_node_entry(t); list_del(&t->rcu_node_entry); if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks) rcu_preempt_ctrlblk.gp_tasks = np; if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks) rcu_preempt_ctrlblk.exp_tasks = np; +#ifdef CONFIG_RCU_BOOST + if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks) + rcu_preempt_ctrlblk.boost_tasks = np; +#endif /* #ifdef CONFIG_RCU_BOOST */ INIT_LIST_HEAD(&t->rcu_node_entry); /* @@ -331,6 +606,14 @@ static void rcu_read_unlock_special(struct task_struct *t) if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL) rcu_report_exp_done(); } +#ifdef CONFIG_RCU_BOOST + /* Unboost self if was boosted. */ + if (special & RCU_READ_UNLOCK_BOOSTED) { + t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED; + rt_mutex_unlock(t->rcu_boost_mutex); + t->rcu_boost_mutex = NULL; + } +#endif /* #ifdef CONFIG_RCU_BOOST */ local_irq_restore(flags); } @@ -374,7 +657,7 @@ static void rcu_preempt_check_callbacks(void) rcu_preempt_cpu_qs(); if (&rcu_preempt_ctrlblk.rcb.rcucblist != rcu_preempt_ctrlblk.rcb.donetail) - raise_softirq(RCU_SOFTIRQ); + invoke_rcu_kthread(); if (rcu_preempt_gp_in_progress() && rcu_cpu_blocking_cur_gp() && rcu_preempt_running_reader()) @@ -383,7 +666,7 @@ static void rcu_preempt_check_callbacks(void) /* * TINY_PREEMPT_RCU has an extra callback-list tail pointer to - * update, so this is invoked from __rcu_process_callbacks() to + * update, so this is invoked from rcu_process_callbacks() to * handle that case. Of course, it is invoked for all flavors of * RCU, but RCU callbacks can appear only on one of the lists, and * neither ->nexttail nor ->donetail can possibly be NULL, so there @@ -400,7 +683,7 @@ static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) */ static void rcu_preempt_process_callbacks(void) { - __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb); + rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb); } /* @@ -417,6 +700,7 @@ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) local_irq_save(flags); *rcu_preempt_ctrlblk.nexttail = head; rcu_preempt_ctrlblk.nexttail = &head->next; + RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++); rcu_preempt_start_gp(); /* checks to see if GP needed. */ local_irq_restore(flags); } @@ -532,6 +816,7 @@ void synchronize_rcu_expedited(void) /* Wait for tail of ->blkd_tasks list to drain. */ if (rcu_preempted_readers_exp()) + rcu_initiate_expedited_boost(); wait_event(sync_rcu_preempt_exp_wq, !rcu_preempted_readers_exp()); @@ -572,6 +857,27 @@ void exit_rcu(void) #else /* #ifdef CONFIG_TINY_PREEMPT_RCU */ +#ifdef CONFIG_RCU_TRACE + +/* + * Because preemptible RCU does not exist, it is not necessary to + * dump out its statistics. + */ +static void show_tiny_preempt_stats(struct seq_file *m) +{ +} + +#endif /* #ifdef CONFIG_RCU_TRACE */ + +/* + * Because preemptible RCU does not exist, it is never necessary to + * boost preempted RCU readers. + */ +static int rcu_boost(void) +{ + return 0; +} + /* * Because preemptible RCU does not exist, it never has any callbacks * to check. @@ -599,17 +905,116 @@ static void rcu_preempt_process_callbacks(void) #endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */ #ifdef CONFIG_DEBUG_LOCK_ALLOC - #include <linux/kernel_stat.h> /* * During boot, we forgive RCU lockdep issues. After this function is * invoked, we start taking RCU lockdep issues seriously. */ -void rcu_scheduler_starting(void) +void __init rcu_scheduler_starting(void) { WARN_ON(nr_context_switches() > 0); rcu_scheduler_active = 1; } #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ + +#ifdef CONFIG_RCU_BOOST +#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO +#else /* #ifdef CONFIG_RCU_BOOST */ +#define RCU_BOOST_PRIO 1 +#endif /* #else #ifdef CONFIG_RCU_BOOST */ + +#ifdef CONFIG_RCU_TRACE + +#ifdef CONFIG_RCU_BOOST + +static void rcu_initiate_boost_trace(void) +{ + if (rcu_preempt_ctrlblk.gp_tasks == NULL) + rcu_preempt_ctrlblk.n_normal_balk_gp_tasks++; + else if (rcu_preempt_ctrlblk.boost_tasks != NULL) + rcu_preempt_ctrlblk.n_normal_balk_boost_tasks++; + else if (rcu_preempt_ctrlblk.boosted_this_gp != 0) + rcu_preempt_ctrlblk.n_normal_balk_boosted++; + else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) + rcu_preempt_ctrlblk.n_normal_balk_notyet++; + else + rcu_preempt_ctrlblk.n_normal_balk_nos++; +} + +static void rcu_initiate_exp_boost_trace(void) +{ + if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) + rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks++; + else + rcu_preempt_ctrlblk.n_exp_balk_nos++; +} + +#endif /* #ifdef CONFIG_RCU_BOOST */ + +static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n) +{ + unsigned long flags; + + raw_local_irq_save(flags); + rcp->qlen -= n; + raw_local_irq_restore(flags); +} + +/* + * Dump statistics for TINY_RCU, such as they are. + */ +static int show_tiny_stats(struct seq_file *m, void *unused) +{ + show_tiny_preempt_stats(m); + seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen); + seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen); + return 0; +} + +static int show_tiny_stats_open(struct inode *inode, struct file *file) +{ + return single_open(file, show_tiny_stats, NULL); +} + +static const struct file_operations show_tiny_stats_fops = { + .owner = THIS_MODULE, + .open = show_tiny_stats_open, + .read = seq_read, + .llseek = seq_lseek, + .release = single_release, +}; + +static struct dentry *rcudir; + +static int __init rcutiny_trace_init(void) +{ + struct dentry *retval; + + rcudir = debugfs_create_dir("rcu", NULL); + if (!rcudir) + goto free_out; + retval = debugfs_create_file("rcudata", 0444, rcudir, + NULL, &show_tiny_stats_fops); + if (!retval) + goto free_out; + return 0; +free_out: + debugfs_remove_recursive(rcudir); + return 1; +} + +static void __exit rcutiny_trace_cleanup(void) +{ + debugfs_remove_recursive(rcudir); +} + +module_init(rcutiny_trace_init); +module_exit(rcutiny_trace_cleanup); + +MODULE_AUTHOR("Paul E. McKenney"); +MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation"); +MODULE_LICENSE("GPL"); + +#endif /* #ifdef CONFIG_RCU_TRACE */ diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 9d8e8fb2515f..89613f97ff26 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -47,6 +47,7 @@ #include <linux/srcu.h> #include <linux/slab.h> #include <asm/byteorder.h> +#include <linux/sched.h> MODULE_LICENSE("GPL"); MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and " @@ -64,6 +65,9 @@ static int irqreader = 1; /* RCU readers from irq (timers). */ static int fqs_duration = 0; /* Duration of bursts (us), 0 to disable. */ static int fqs_holdoff = 0; /* Hold time within burst (us). */ static int fqs_stutter = 3; /* Wait time between bursts (s). */ +static int test_boost = 1; /* Test RCU prio boost: 0=no, 1=maybe, 2=yes. */ +static int test_boost_interval = 7; /* Interval between boost tests, seconds. */ +static int test_boost_duration = 4; /* Duration of each boost test, seconds. */ static char *torture_type = "rcu"; /* What RCU implementation to torture. */ module_param(nreaders, int, 0444); @@ -88,6 +92,12 @@ module_param(fqs_holdoff, int, 0444); MODULE_PARM_DESC(fqs_holdoff, "Holdoff time within fqs bursts (us)"); module_param(fqs_stutter, int, 0444); MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)"); +module_param(test_boost, int, 0444); +MODULE_PARM_DESC(test_boost, "Test RCU prio boost: 0=no, 1=maybe, 2=yes."); +module_param(test_boost_interval, int, 0444); +MODULE_PARM_DESC(test_boost_interval, "Interval between boost tests, seconds."); +module_param(test_boost_duration, int, 0444); +MODULE_PARM_DESC(test_boost_duration, "Duration of each boost test, seconds."); module_param(torture_type, charp, 0444); MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, srcu)"); @@ -109,6 +119,7 @@ static struct task_struct *stats_task; static struct task_struct *shuffler_task; static struct task_struct *stutter_task; static struct task_struct *fqs_task; +static struct task_struct *boost_tasks[NR_CPUS]; #define RCU_TORTURE_PIPE_LEN 10 @@ -134,6 +145,12 @@ static atomic_t n_rcu_torture_alloc_fail; static atomic_t n_rcu_torture_free; static atomic_t n_rcu_torture_mberror; static atomic_t n_rcu_torture_error; +static long n_rcu_torture_boost_ktrerror; +static long n_rcu_torture_boost_rterror; +static long n_rcu_torture_boost_allocerror; +static long n_rcu_torture_boost_afferror; +static long n_rcu_torture_boost_failure; +static long n_rcu_torture_boosts; static long n_rcu_torture_timers; static struct list_head rcu_torture_removed; static cpumask_var_t shuffle_tmp_mask; @@ -147,6 +164,16 @@ static int stutter_pause_test; #endif int rcutorture_runnable = RCUTORTURE_RUNNABLE_INIT; +#ifdef CONFIG_RCU_BOOST +#define rcu_can_boost() 1 +#else /* #ifdef CONFIG_RCU_BOOST */ +#define rcu_can_boost() 0 +#endif /* #else #ifdef CONFIG_RCU_BOOST */ + +static unsigned long boost_starttime; /* jiffies of next boost test start. */ +DEFINE_MUTEX(boost_mutex); /* protect setting boost_starttime */ + /* and boost task create/destroy. */ + /* Mediate rmmod and system shutdown. Concurrent rmmod & shutdown illegal! */ #define FULLSTOP_DONTSTOP 0 /* Normal operation. */ @@ -277,6 +304,7 @@ struct rcu_torture_ops { void (*fqs)(void); int (*stats)(char *page); int irq_capable; + int can_boost; char *name; }; @@ -366,6 +394,7 @@ static struct rcu_torture_ops rcu_ops = { .fqs = rcu_force_quiescent_state, .stats = NULL, .irq_capable = 1, + .can_boost = rcu_can_boost(), .name = "rcu" }; @@ -408,6 +437,7 @@ static struct rcu_torture_ops rcu_sync_ops = { .fqs = rcu_force_quiescent_state, .stats = NULL, .irq_capable = 1, + .can_boost = rcu_can_boost(), .name = "rcu_sync" }; @@ -424,6 +454,7 @@ static struct rcu_torture_ops rcu_expedited_ops = { .fqs = rcu_force_quiescent_state, .stats = NULL, .irq_capable = 1, + .can_boost = rcu_can_boost(), .name = "rcu_expedited" }; @@ -684,6 +715,110 @@ static struct rcu_torture_ops sched_expedited_ops = { }; /* + * RCU torture priority-boost testing. Runs one real-time thread per + * CPU for moderate bursts, repeatedly registering RCU callbacks and + * spinning waiting for them to be invoked. If a given callback takes + * too long to be invoked, we assume that priority inversion has occurred. + */ + +struct rcu_boost_inflight { + struct rcu_head rcu; + int inflight; +}; + +static void rcu_torture_boost_cb(struct rcu_head *head) +{ + struct rcu_boost_inflight *rbip = + container_of(head, struct rcu_boost_inflight, rcu); + + smp_mb(); /* Ensure RCU-core accesses precede clearing ->inflight */ + rbip->inflight = 0; +} + +static int rcu_torture_boost(void *arg) +{ + unsigned long call_rcu_time; + unsigned long endtime; + unsigned long oldstarttime; + struct rcu_boost_inflight rbi = { .inflight = 0 }; + struct sched_param sp; + + VERBOSE_PRINTK_STRING("rcu_torture_boost started"); + + /* Set real-time priority. */ + sp.sched_priority = 1; + if (sched_setscheduler(current, SCHED_FIFO, &sp) < 0) { + VERBOSE_PRINTK_STRING("rcu_torture_boost RT prio failed!"); + n_rcu_torture_boost_rterror++; + } + + /* Each pass through the following loop does one boost-test cycle. */ + do { + /* Wait for the next test interval. */ + oldstarttime = boost_starttime; + while (jiffies - oldstarttime > ULONG_MAX / 2) { + schedule_timeout_uninterruptible(1); + rcu_stutter_wait("rcu_torture_boost"); + if (kthread_should_stop() || + fullstop != FULLSTOP_DONTSTOP) + goto checkwait; + } + + /* Do one boost-test interval. */ + endtime = oldstarttime + test_boost_duration * HZ; + call_rcu_time = jiffies; + while (jiffies - endtime > ULONG_MAX / 2) { + /* If we don't have a callback in flight, post one. */ + if (!rbi.inflight) { + smp_mb(); /* RCU core before ->inflight = 1. */ + rbi.inflight = 1; + call_rcu(&rbi.rcu, rcu_torture_boost_cb); + if (jiffies - call_rcu_time > + test_boost_duration * HZ - HZ / 2) { + VERBOSE_PRINTK_STRING("rcu_torture_boost boosting failed"); + n_rcu_torture_boost_failure++; + } + call_rcu_time = jiffies; + } + cond_resched(); + rcu_stutter_wait("rcu_torture_boost"); + if (kthread_should_stop() || + fullstop != FULLSTOP_DONTSTOP) + goto checkwait; + } + + /* + * Set the start time of the next test interval. + * Yes, this is vulnerable to long delays, but such + * delays simply cause a false negative for the next + * interval. Besides, we are running at RT priority, + * so delays should be relatively rare. + */ + while (oldstarttime == boost_starttime) { + if (mutex_trylock(&boost_mutex)) { + boost_starttime = jiffies + + test_boost_interval * HZ; + n_rcu_torture_boosts++; + mutex_unlock(&boost_mutex); + break; + } + schedule_timeout_uninterruptible(1); + } + + /* Go do the stutter. */ +checkwait: rcu_stutter_wait("rcu_torture_boost"); + } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP); + + /* Clean up and exit. */ + VERBOSE_PRINTK_STRING("rcu_torture_boost task stopping"); + rcutorture_shutdown_absorb("rcu_torture_boost"); + while (!kthread_should_stop() || rbi.inflight) + schedule_timeout_uninterruptible(1); + smp_mb(); /* order accesses to ->inflight before stack-frame death. */ + return 0; +} + +/* * RCU torture force-quiescent-state kthread. Repeatedly induces * bursts of calls to force_quiescent_state(), increasing the probability * of occurrence of some important types of race conditions. @@ -933,7 +1068,8 @@ rcu_torture_printk(char *page) cnt += sprintf(&page[cnt], "%s%s ", torture_type, TORTURE_FLAG); cnt += sprintf(&page[cnt], "rtc: %p ver: %ld tfle: %d rta: %d rtaf: %d rtf: %d " - "rtmbe: %d nt: %ld", + "rtmbe: %d rtbke: %ld rtbre: %ld rtbae: %ld rtbafe: %ld " + "rtbf: %ld rtb: %ld nt: %ld", rcu_torture_current, rcu_torture_current_version, list_empty(&rcu_torture_freelist), @@ -941,8 +1077,19 @@ rcu_torture_printk(char *page) atomic_read(&n_rcu_torture_alloc_fail), atomic_read(&n_rcu_torture_free), atomic_read(&n_rcu_torture_mberror), + n_rcu_torture_boost_ktrerror, + n_rcu_torture_boost_rterror, + n_rcu_torture_boost_allocerror, + n_rcu_torture_boost_afferror, + n_rcu_torture_boost_failure, + n_rcu_torture_boosts, n_rcu_torture_timers); - if (atomic_read(&n_rcu_torture_mberror) != 0) + if (atomic_read(&n_rcu_torture_mberror) != 0 || + n_rcu_torture_boost_ktrerror != 0 || + n_rcu_torture_boost_rterror != 0 || + n_rcu_torture_boost_allocerror != 0 || + n_rcu_torture_boost_afferror != 0 || + n_rcu_torture_boost_failure != 0) cnt += sprintf(&page[cnt], " !!!"); cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG); if (i > 1) { @@ -1094,22 +1241,91 @@ rcu_torture_stutter(void *arg) } static inline void -rcu_torture_print_module_parms(char *tag) +rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag) { printk(KERN_ALERT "%s" TORTURE_FLAG "--- %s: nreaders=%d nfakewriters=%d " "stat_interval=%d verbose=%d test_no_idle_hz=%d " "shuffle_interval=%d stutter=%d irqreader=%d " - "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d\n", + "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d " + "test_boost=%d/%d test_boost_interval=%d " + "test_boost_duration=%d\n", torture_type, tag, nrealreaders, nfakewriters, stat_interval, verbose, test_no_idle_hz, shuffle_interval, - stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter); + stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter, + test_boost, cur_ops->can_boost, + test_boost_interval, test_boost_duration); } -static struct notifier_block rcutorture_nb = { +static struct notifier_block rcutorture_shutdown_nb = { .notifier_call = rcutorture_shutdown_notify, }; +static void rcutorture_booster_cleanup(int cpu) +{ + struct task_struct *t; + + if (boost_tasks[cpu] == NULL) + return; + mutex_lock(&boost_mutex); + VERBOSE_PRINTK_STRING("Stopping rcu_torture_boost task"); + t = boost_tasks[cpu]; + boost_tasks[cpu] = NULL; + mutex_unlock(&boost_mutex); + + /* This must be outside of the mutex, otherwise deadlock! */ + kthread_stop(t); +} + +static int rcutorture_booster_init(int cpu) +{ + int retval; + + if (boost_tasks[cpu] != NULL) + return 0; /* Already created, nothing more to do. */ + + /* Don't allow time recalculation while creating a new task. */ + mutex_lock(&boost_mutex); + VERBOSE_PRINTK_STRING("Creating rcu_torture_boost task"); + boost_tasks[cpu] = kthread_create(rcu_torture_boost, NULL, + "rcu_torture_boost"); + if (IS_ERR(boost_tasks[cpu])) { + retval = PTR_ERR(boost_tasks[cpu]); + VERBOSE_PRINTK_STRING("rcu_torture_boost task create failed"); + n_rcu_torture_boost_ktrerror++; + boost_tasks[cpu] = NULL; + mutex_unlock(&boost_mutex); + return retval; + } + kthread_bind(boost_tasks[cpu], cpu); + wake_up_process(boost_tasks[cpu]); + mutex_unlock(&boost_mutex); + return 0; +} + +static int rcutorture_cpu_notify(struct notifier_block *self, + unsigned long action, void *hcpu) +{ + long cpu = (long)hcpu; + + switch (action) { + case CPU_ONLINE: + case CPU_DOWN_FAILED: + (void)rcutorture_booster_init(cpu); + break; + case CPU_DOWN_PREPARE: + rcutorture_booster_cleanup(cpu); + break; + default: + break; + } + return NOTIFY_OK; +} + +static struct notifier_block rcutorture_cpu_nb = { + .notifier_call = rcutorture_cpu_notify, +}; + static void rcu_torture_cleanup(void) { @@ -1127,7 +1343,7 @@ rcu_torture_cleanup(void) } fullstop = FULLSTOP_RMMOD; mutex_unlock(&fullstop_mutex); - unregister_reboot_notifier(&rcutorture_nb); + unregister_reboot_notifier(&rcutorture_shutdown_nb); if (stutter_task) { VERBOSE_PRINTK_STRING("Stopping rcu_torture_stutter task"); kthread_stop(stutter_task); @@ -1184,6 +1400,12 @@ rcu_torture_cleanup(void) kthread_stop(fqs_task); } fqs_task = NULL; + if ((test_boost == 1 && cur_ops->can_boost) || + test_boost == 2) { + unregister_cpu_notifier(&rcutorture_cpu_nb); + for_each_possible_cpu(i) + rcutorture_booster_cleanup(i); + } /* Wait for all RCU callbacks to fire. */ @@ -1195,9 +1417,9 @@ rcu_torture_cleanup(void) if (cur_ops->cleanup) cur_ops->cleanup(); if (atomic_read(&n_rcu_torture_error)) - rcu_torture_print_module_parms("End of test: FAILURE"); + rcu_torture_print_module_parms(cur_ops, "End of test: FAILURE"); else - rcu_torture_print_module_parms("End of test: SUCCESS"); + rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS"); } static int __init @@ -1242,7 +1464,7 @@ rcu_torture_init(void) nrealreaders = nreaders; else nrealreaders = 2 * num_online_cpus(); - rcu_torture_print_module_parms("Start of test"); + rcu_torture_print_module_parms(cur_ops, "Start of test"); fullstop = FULLSTOP_DONTSTOP; /* Set up the freelist. */ @@ -1263,6 +1485,12 @@ rcu_torture_init(void) atomic_set(&n_rcu_torture_free, 0); atomic_set(&n_rcu_torture_mberror, 0); atomic_set(&n_rcu_torture_error, 0); + n_rcu_torture_boost_ktrerror = 0; + n_rcu_torture_boost_rterror = 0; + n_rcu_torture_boost_allocerror = 0; + n_rcu_torture_boost_afferror = 0; + n_rcu_torture_boost_failure = 0; + n_rcu_torture_boosts = 0; for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) atomic_set(&rcu_torture_wcount[i], 0); for_each_possible_cpu(cpu) { @@ -1376,7 +1604,27 @@ rcu_torture_init(void) goto unwind; } } - register_reboot_notifier(&rcutorture_nb); + if (test_boost_interval < 1) + test_boost_interval = 1; + if (test_boost_duration < 2) + test_boost_duration = 2; + if ((test_boost == 1 && cur_ops->can_boost) || + test_boost == 2) { + int retval; + + boost_starttime = jiffies + test_boost_interval * HZ; + register_cpu_notifier(&rcutorture_cpu_nb); + for_each_possible_cpu(i) { + if (cpu_is_offline(i)) + continue; /* Heuristic: CPU can go offline. */ + retval = rcutorture_booster_init(i); + if (retval < 0) { + firsterr = retval; + goto unwind; + } + } + } + register_reboot_notifier(&rcutorture_shutdown_nb); mutex_unlock(&fullstop_mutex); return 0; diff --git a/kernel/rcutree.c b/kernel/rcutree.c index ccdc04c47981..d0ddfea6579d 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -67,9 +67,6 @@ static struct lock_class_key rcu_node_class[NUM_RCU_LVLS]; .gpnum = -300, \ .completed = -300, \ .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname.onofflock), \ - .orphan_cbs_list = NULL, \ - .orphan_cbs_tail = &structname.orphan_cbs_list, \ - .orphan_qlen = 0, \ .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname.fqslock), \ .n_force_qs = 0, \ .n_force_qs_ngp = 0, \ @@ -620,9 +617,17 @@ static void __init check_cpu_stall_init(void) static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { if (rdp->gpnum != rnp->gpnum) { - rdp->qs_pending = 1; - rdp->passed_quiesc = 0; + /* + * If the current grace period is waiting for this CPU, + * set up to detect a quiescent state, otherwise don't + * go looking for one. + */ rdp->gpnum = rnp->gpnum; + if (rnp->qsmask & rdp->grpmask) { + rdp->qs_pending = 1; + rdp->passed_quiesc = 0; + } else + rdp->qs_pending = 0; } } @@ -681,6 +686,24 @@ __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat /* Remember that we saw this grace-period completion. */ rdp->completed = rnp->completed; + + /* + * If we were in an extended quiescent state, we may have + * missed some grace periods that others CPUs handled on + * our behalf. Catch up with this state to avoid noting + * spurious new grace periods. If another grace period + * has started, then rnp->gpnum will have advanced, so + * we will detect this later on. + */ + if (ULONG_CMP_LT(rdp->gpnum, rdp->completed)) + rdp->gpnum = rdp->completed; + + /* + * If RCU does not need a quiescent state from this CPU, + * then make sure that this CPU doesn't go looking for one. + */ + if ((rnp->qsmask & rdp->grpmask) == 0) + rdp->qs_pending = 0; } } @@ -984,53 +1007,31 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) #ifdef CONFIG_HOTPLUG_CPU /* - * Move a dying CPU's RCU callbacks to the ->orphan_cbs_list for the - * specified flavor of RCU. The callbacks will be adopted by the next - * _rcu_barrier() invocation or by the CPU_DEAD notifier, whichever - * comes first. Because this is invoked from the CPU_DYING notifier, - * irqs are already disabled. + * Move a dying CPU's RCU callbacks to online CPU's callback list. + * Synchronization is not required because this function executes + * in stop_machine() context. */ -static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp) +static void rcu_send_cbs_to_online(struct rcu_state *rsp) { int i; + /* current DYING CPU is cleared in the cpu_online_mask */ + int receive_cpu = cpumask_any(cpu_online_mask); struct rcu_data *rdp = this_cpu_ptr(rsp->rda); + struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu); if (rdp->nxtlist == NULL) return; /* irqs disabled, so comparison is stable. */ - raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ - *rsp->orphan_cbs_tail = rdp->nxtlist; - rsp->orphan_cbs_tail = rdp->nxttail[RCU_NEXT_TAIL]; + + *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist; + receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; + receive_rdp->qlen += rdp->qlen; + receive_rdp->n_cbs_adopted += rdp->qlen; + rdp->n_cbs_orphaned += rdp->qlen; + rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; - rsp->orphan_qlen += rdp->qlen; - rdp->n_cbs_orphaned += rdp->qlen; rdp->qlen = 0; - raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ -} - -/* - * Adopt previously orphaned RCU callbacks. - */ -static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) -{ - unsigned long flags; - struct rcu_data *rdp; - - raw_spin_lock_irqsave(&rsp->onofflock, flags); - rdp = this_cpu_ptr(rsp->rda); - if (rsp->orphan_cbs_list == NULL) { - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); - return; - } - *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_list; - rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_tail; - rdp->qlen += rsp->orphan_qlen; - rdp->n_cbs_adopted += rsp->orphan_qlen; - rsp->orphan_cbs_list = NULL; - rsp->orphan_cbs_tail = &rsp->orphan_cbs_list; - rsp->orphan_qlen = 0; - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); } /* @@ -1081,8 +1082,6 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) raw_spin_unlock_irqrestore(&rnp->lock, flags); if (need_report & RCU_OFL_TASKS_EXP_GP) rcu_report_exp_rnp(rsp, rnp); - - rcu_adopt_orphan_cbs(rsp); } /* @@ -1100,11 +1099,7 @@ static void rcu_offline_cpu(int cpu) #else /* #ifdef CONFIG_HOTPLUG_CPU */ -static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp) -{ -} - -static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) +static void rcu_send_cbs_to_online(struct rcu_state *rsp) { } @@ -1440,22 +1435,11 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), */ local_irq_save(flags); rdp = this_cpu_ptr(rsp->rda); - rcu_process_gp_end(rsp, rdp); - check_for_new_grace_period(rsp, rdp); /* Add the callback to our list. */ *rdp->nxttail[RCU_NEXT_TAIL] = head; rdp->nxttail[RCU_NEXT_TAIL] = &head->next; - /* Start a new grace period if one not already started. */ - if (!rcu_gp_in_progress(rsp)) { - unsigned long nestflag; - struct rcu_node *rnp_root = rcu_get_root(rsp); - - raw_spin_lock_irqsave(&rnp_root->lock, nestflag); - rcu_start_gp(rsp, nestflag); /* releases rnp_root->lock. */ - } - /* * Force the grace period if too many callbacks or too long waiting. * Enforce hysteresis, and don't invoke force_quiescent_state() @@ -1464,12 +1448,27 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), * is the only one waiting for a grace period to complete. */ if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) { - rdp->blimit = LONG_MAX; - if (rsp->n_force_qs == rdp->n_force_qs_snap && - *rdp->nxttail[RCU_DONE_TAIL] != head) - force_quiescent_state(rsp, 0); - rdp->n_force_qs_snap = rsp->n_force_qs; - rdp->qlen_last_fqs_check = rdp->qlen; + + /* Are we ignoring a completed grace period? */ + rcu_process_gp_end(rsp, rdp); + check_for_new_grace_period(rsp, rdp); + + /* Start a new grace period if one not already started. */ + if (!rcu_gp_in_progress(rsp)) { + unsigned long nestflag; + struct rcu_node *rnp_root = rcu_get_root(rsp); + + raw_spin_lock_irqsave(&rnp_root->lock, nestflag); + rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */ + } else { + /* Give the grace period a kick. */ + rdp->blimit = LONG_MAX; + if (rsp->n_force_qs == rdp->n_force_qs_snap && + *rdp->nxttail[RCU_DONE_TAIL] != head) + force_quiescent_state(rsp, 0); + rdp->n_force_qs_snap = rsp->n_force_qs; + rdp->qlen_last_fqs_check = rdp->qlen; + } } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) force_quiescent_state(rsp, 1); local_irq_restore(flags); @@ -1699,13 +1698,12 @@ static void _rcu_barrier(struct rcu_state *rsp, * decrement rcu_barrier_cpu_count -- otherwise the first CPU * might complete its grace period before all of the other CPUs * did their increment, causing this function to return too - * early. + * early. Note that on_each_cpu() disables irqs, which prevents + * any CPUs from coming online or going offline until each online + * CPU has queued its RCU-barrier callback. */ atomic_set(&rcu_barrier_cpu_count, 1); - preempt_disable(); /* stop CPU_DYING from filling orphan_cbs_list */ - rcu_adopt_orphan_cbs(rsp); on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1); - preempt_enable(); /* CPU_DYING can again fill orphan_cbs_list */ if (atomic_dec_and_test(&rcu_barrier_cpu_count)) complete(&rcu_barrier_completion); wait_for_completion(&rcu_barrier_completion); @@ -1831,18 +1829,13 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, case CPU_DYING: case CPU_DYING_FROZEN: /* - * preempt_disable() in _rcu_barrier() prevents stop_machine(), - * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);" - * returns, all online cpus have queued rcu_barrier_func(). - * The dying CPU clears its cpu_online_mask bit and - * moves all of its RCU callbacks to ->orphan_cbs_list - * in the context of stop_machine(), so subsequent calls - * to _rcu_barrier() will adopt these callbacks and only - * then queue rcu_barrier_func() on all remaining CPUs. + * The whole machine is "stopped" except this CPU, so we can + * touch any data without introducing corruption. We send the + * dying CPU's callbacks to an arbitrarily chosen online CPU. */ - rcu_send_cbs_to_orphanage(&rcu_bh_state); - rcu_send_cbs_to_orphanage(&rcu_sched_state); - rcu_preempt_send_cbs_to_orphanage(); + rcu_send_cbs_to_online(&rcu_bh_state); + rcu_send_cbs_to_online(&rcu_sched_state); + rcu_preempt_send_cbs_to_online(); break; case CPU_DEAD: case CPU_DEAD_FROZEN: @@ -1880,8 +1873,9 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp) { int i; - for (i = NUM_RCU_LVLS - 1; i >= 0; i--) + for (i = NUM_RCU_LVLS - 1; i > 0; i--) rsp->levelspread[i] = CONFIG_RCU_FANOUT; + rsp->levelspread[0] = RCU_FANOUT_LEAF; } #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */ static void __init rcu_init_levelspread(struct rcu_state *rsp) diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 91d4170c5c13..e8f057e44e3e 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -31,46 +31,51 @@ /* * Define shape of hierarchy based on NR_CPUS and CONFIG_RCU_FANOUT. * In theory, it should be possible to add more levels straightforwardly. - * In practice, this has not been tested, so there is probably some - * bug somewhere. + * In practice, this did work well going from three levels to four. + * Of course, your mileage may vary. */ #define MAX_RCU_LVLS 4 -#define RCU_FANOUT (CONFIG_RCU_FANOUT) -#define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT) -#define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT) -#define RCU_FANOUT_FOURTH (RCU_FANOUT_CUBE * RCU_FANOUT) - -#if NR_CPUS <= RCU_FANOUT +#if CONFIG_RCU_FANOUT > 16 +#define RCU_FANOUT_LEAF 16 +#else /* #if CONFIG_RCU_FANOUT > 16 */ +#define RCU_FANOUT_LEAF (CONFIG_RCU_FANOUT) +#endif /* #else #if CONFIG_RCU_FANOUT > 16 */ +#define RCU_FANOUT_1 (RCU_FANOUT_LEAF) +#define RCU_FANOUT_2 (RCU_FANOUT_1 * CONFIG_RCU_FANOUT) +#define RCU_FANOUT_3 (RCU_FANOUT_2 * CONFIG_RCU_FANOUT) +#define RCU_FANOUT_4 (RCU_FANOUT_3 * CONFIG_RCU_FANOUT) + +#if NR_CPUS <= RCU_FANOUT_1 # define NUM_RCU_LVLS 1 # define NUM_RCU_LVL_0 1 # define NUM_RCU_LVL_1 (NR_CPUS) # define NUM_RCU_LVL_2 0 # define NUM_RCU_LVL_3 0 # define NUM_RCU_LVL_4 0 -#elif NR_CPUS <= RCU_FANOUT_SQ +#elif NR_CPUS <= RCU_FANOUT_2 # define NUM_RCU_LVLS 2 # define NUM_RCU_LVL_0 1 -# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT) +# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) # define NUM_RCU_LVL_2 (NR_CPUS) # define NUM_RCU_LVL_3 0 # define NUM_RCU_LVL_4 0 -#elif NR_CPUS <= RCU_FANOUT_CUBE +#elif NR_CPUS <= RCU_FANOUT_3 # define NUM_RCU_LVLS 3 # define NUM_RCU_LVL_0 1 -# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_SQ) -# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT) -# define NUM_RCU_LVL_3 NR_CPUS +# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2) +# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) +# define NUM_RCU_LVL_3 (NR_CPUS) # define NUM_RCU_LVL_4 0 -#elif NR_CPUS <= RCU_FANOUT_FOURTH +#elif NR_CPUS <= RCU_FANOUT_4 # define NUM_RCU_LVLS 4 # define NUM_RCU_LVL_0 1 -# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_CUBE) -# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_SQ) -# define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT) -# define NUM_RCU_LVL_4 NR_CPUS +# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3) +# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2) +# define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) +# define NUM_RCU_LVL_4 (NR_CPUS) #else # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS" -#endif /* #if (NR_CPUS) <= RCU_FANOUT */ +#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */ #define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3 + NUM_RCU_LVL_4) #define NUM_RCU_NODES (RCU_SUM - NR_CPUS) @@ -203,8 +208,8 @@ struct rcu_data { long qlen_last_fqs_check; /* qlen at last check for QS forcing */ unsigned long n_cbs_invoked; /* count of RCU cbs invoked. */ - unsigned long n_cbs_orphaned; /* RCU cbs sent to orphanage. */ - unsigned long n_cbs_adopted; /* RCU cbs adopted from orphanage. */ + unsigned long n_cbs_orphaned; /* RCU cbs orphaned by dying CPU */ + unsigned long n_cbs_adopted; /* RCU cbs adopted from dying CPU */ unsigned long n_force_qs_snap; /* did other CPU force QS recently? */ long blimit; /* Upper limit on a processed batch */ @@ -309,15 +314,7 @@ struct rcu_state { /* End of fields guarded by root rcu_node's lock. */ raw_spinlock_t onofflock; /* exclude on/offline and */ - /* starting new GP. Also */ - /* protects the following */ - /* orphan_cbs fields. */ - struct rcu_head *orphan_cbs_list; /* list of rcu_head structs */ - /* orphaned by all CPUs in */ - /* a given leaf rcu_node */ - /* going offline. */ - struct rcu_head **orphan_cbs_tail; /* And tail pointer. */ - long orphan_qlen; /* Number of orphaned cbs. */ + /* starting new GP. */ raw_spinlock_t fqslock; /* Only one task forcing */ /* quiescent states. */ unsigned long jiffies_force_qs; /* Time at which to invoke */ @@ -390,7 +387,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp); static int rcu_preempt_pending(int cpu); static int rcu_preempt_needs_cpu(int cpu); static void __cpuinit rcu_preempt_init_percpu_data(int cpu); -static void rcu_preempt_send_cbs_to_orphanage(void); +static void rcu_preempt_send_cbs_to_online(void); static void __init __rcu_init_preempt(void); static void rcu_needs_cpu_flush(void); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 71a4147473f9..a3638710dc67 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -25,6 +25,7 @@ */ #include <linux/delay.h> +#include <linux/stop_machine.h> /* * Check the RCU kernel configuration parameters and print informative @@ -773,11 +774,11 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) } /* - * Move preemptable RCU's callbacks to ->orphan_cbs_list. + * Move preemptable RCU's callbacks from dying CPU to other online CPU. */ -static void rcu_preempt_send_cbs_to_orphanage(void) +static void rcu_preempt_send_cbs_to_online(void) { - rcu_send_cbs_to_orphanage(&rcu_preempt_state); + rcu_send_cbs_to_online(&rcu_preempt_state); } /* @@ -1001,7 +1002,7 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) /* * Because there is no preemptable RCU, there are no callbacks to move. */ -static void rcu_preempt_send_cbs_to_orphanage(void) +static void rcu_preempt_send_cbs_to_online(void) { } @@ -1014,6 +1015,132 @@ static void __init __rcu_init_preempt(void) #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ +#ifndef CONFIG_SMP + +void synchronize_sched_expedited(void) +{ + cond_resched(); +} +EXPORT_SYMBOL_GPL(synchronize_sched_expedited); + +#else /* #ifndef CONFIG_SMP */ + +static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); +static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); + +static int synchronize_sched_expedited_cpu_stop(void *data) +{ + /* + * There must be a full memory barrier on each affected CPU + * between the time that try_stop_cpus() is called and the + * time that it returns. + * + * In the current initial implementation of cpu_stop, the + * above condition is already met when the control reaches + * this point and the following smp_mb() is not strictly + * necessary. Do smp_mb() anyway for documentation and + * robustness against future implementation changes. + */ + smp_mb(); /* See above comment block. */ + return 0; +} + +/* + * Wait for an rcu-sched grace period to elapse, but use "big hammer" + * approach to force grace period to end quickly. This consumes + * significant time on all CPUs, and is thus not recommended for + * any sort of common-case code. + * + * Note that it is illegal to call this function while holding any + * lock that is acquired by a CPU-hotplug notifier. Failing to + * observe this restriction will result in deadlock. + * + * This implementation can be thought of as an application of ticket + * locking to RCU, with sync_sched_expedited_started and + * sync_sched_expedited_done taking on the roles of the halves + * of the ticket-lock word. Each task atomically increments + * sync_sched_expedited_started upon entry, snapshotting the old value, + * then attempts to stop all the CPUs. If this succeeds, then each + * CPU will have executed a context switch, resulting in an RCU-sched + * grace period. We are then done, so we use atomic_cmpxchg() to + * update sync_sched_expedited_done to match our snapshot -- but + * only if someone else has not already advanced past our snapshot. + * + * On the other hand, if try_stop_cpus() fails, we check the value + * of sync_sched_expedited_done. If it has advanced past our + * initial snapshot, then someone else must have forced a grace period + * some time after we took our snapshot. In this case, our work is + * done for us, and we can simply return. Otherwise, we try again, + * but keep our initial snapshot for purposes of checking for someone + * doing our work for us. + * + * If we fail too many times in a row, we fall back to synchronize_sched(). + */ +void synchronize_sched_expedited(void) +{ + int firstsnap, s, snap, trycount = 0; + + /* Note that atomic_inc_return() implies full memory barrier. */ + firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); + get_online_cpus(); + + /* + * Each pass through the following loop attempts to force a + * context switch on each CPU. + */ + while (try_stop_cpus(cpu_online_mask, + synchronize_sched_expedited_cpu_stop, + NULL) == -EAGAIN) { + put_online_cpus(); + + /* No joy, try again later. Or just synchronize_sched(). */ + if (trycount++ < 10) + udelay(trycount * num_online_cpus()); + else { + synchronize_sched(); + return; + } + + /* Check to see if someone else did our work for us. */ + s = atomic_read(&sync_sched_expedited_done); + if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) { + smp_mb(); /* ensure test happens before caller kfree */ + return; + } + + /* + * Refetching sync_sched_expedited_started allows later + * callers to piggyback on our grace period. We subtract + * 1 to get the same token that the last incrementer got. + * We retry after they started, so our grace period works + * for them, and they started after our first try, so their + * grace period works for us. + */ + get_online_cpus(); + snap = atomic_read(&sync_sched_expedited_started) - 1; + smp_mb(); /* ensure read is before try_stop_cpus(). */ + } + + /* + * Everyone up to our most recent fetch is covered by our grace + * period. Update the counter, but only if our work is still + * relevant -- which it won't be if someone who started later + * than we did beat us to the punch. + */ + do { + s = atomic_read(&sync_sched_expedited_done); + if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) { + smp_mb(); /* ensure test happens before caller kfree */ + break; + } + } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s); + + put_online_cpus(); +} +EXPORT_SYMBOL_GPL(synchronize_sched_expedited); + +#endif /* #else #ifndef CONFIG_SMP */ + #if !defined(CONFIG_RCU_FAST_NO_HZ) /* diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index d15430b9d122..c8e97853b970 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -166,13 +166,13 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp) gpnum = rsp->gpnum; seq_printf(m, "c=%lu g=%lu s=%d jfq=%ld j=%x " - "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld\n", + "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu\n", rsp->completed, gpnum, rsp->signaled, (long)(rsp->jiffies_force_qs - jiffies), (int)(jiffies & 0xffff), rsp->n_force_qs, rsp->n_force_qs_ngp, rsp->n_force_qs - rsp->n_force_qs_ngp, - rsp->n_force_qs_lh, rsp->orphan_qlen); + rsp->n_force_qs_lh); for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < NUM_RCU_NODES; rnp++) { if (rnp->level != level) { seq_puts(m, "\n"); @@ -300,7 +300,7 @@ static const struct file_operations rcu_pending_fops = { static struct dentry *rcudir; -static int __init rcuclassic_trace_init(void) +static int __init rcutree_trace_init(void) { struct dentry *retval; @@ -337,14 +337,14 @@ free_out: return 1; } -static void __exit rcuclassic_trace_cleanup(void) +static void __exit rcutree_trace_cleanup(void) { debugfs_remove_recursive(rcudir); } -module_init(rcuclassic_trace_init); -module_exit(rcuclassic_trace_cleanup); +module_init(rcutree_trace_init); +module_exit(rcutree_trace_cleanup); MODULE_AUTHOR("Paul E. McKenney"); MODULE_DESCRIPTION("Read-Copy Update tracing for hierarchical implementation"); diff --git a/kernel/sched.c b/kernel/sched.c index 297d1a0eedb0..e6f8f1254319 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -9534,72 +9534,3 @@ struct cgroup_subsys cpuacct_subsys = { }; #endif /* CONFIG_CGROUP_CPUACCT */ -#ifndef CONFIG_SMP - -void synchronize_sched_expedited(void) -{ - barrier(); -} -EXPORT_SYMBOL_GPL(synchronize_sched_expedited); - -#else /* #ifndef CONFIG_SMP */ - -static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0); - -static int synchronize_sched_expedited_cpu_stop(void *data) -{ - /* - * There must be a full memory barrier on each affected CPU - * between the time that try_stop_cpus() is called and the - * time that it returns. - * - * In the current initial implementation of cpu_stop, the - * above condition is already met when the control reaches - * this point and the following smp_mb() is not strictly - * necessary. Do smp_mb() anyway for documentation and - * robustness against future implementation changes. - */ - smp_mb(); /* See above comment block. */ - return 0; -} - -/* - * Wait for an rcu-sched grace period to elapse, but use "big hammer" - * approach to force grace period to end quickly. This consumes - * significant time on all CPUs, and is thus not recommended for - * any sort of common-case code. - * - * Note that it is illegal to call this function while holding any - * lock that is acquired by a CPU-hotplug notifier. Failing to - * observe this restriction will result in deadlock. - */ -void synchronize_sched_expedited(void) -{ - int snap, trycount = 0; - - smp_mb(); /* ensure prior mod happens before capturing snap. */ - snap = atomic_read(&synchronize_sched_expedited_count) + 1; - get_online_cpus(); - while (try_stop_cpus(cpu_online_mask, - synchronize_sched_expedited_cpu_stop, - NULL) == -EAGAIN) { - put_online_cpus(); - if (trycount++ < 10) - udelay(trycount * num_online_cpus()); - else { - synchronize_sched(); - return; - } - if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) { - smp_mb(); /* ensure test happens before caller kfree */ - return; - } - get_online_cpus(); - } - atomic_inc(&synchronize_sched_expedited_count); - smp_mb__after_atomic_inc(); /* ensure post-GP actions seen after GP. */ - put_online_cpus(); -} -EXPORT_SYMBOL_GPL(synchronize_sched_expedited); - -#endif /* #else #ifndef CONFIG_SMP */ diff --git a/kernel/srcu.c b/kernel/srcu.c index c71e07500536..98d8c1e80edb 100644 --- a/kernel/srcu.c +++ b/kernel/srcu.c @@ -31,6 +31,7 @@ #include <linux/rcupdate.h> #include <linux/sched.h> #include <linux/smp.h> +#include <linux/delay.h> #include <linux/srcu.h> static int init_srcu_struct_fields(struct srcu_struct *sp) @@ -203,9 +204,14 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void)) * all srcu_read_lock() calls using the old counters have completed. * Their corresponding critical sections might well be still * executing, but the srcu_read_lock() primitives themselves - * will have finished executing. + * will have finished executing. We initially give readers + * an arbitrarily chosen 10 microseconds to get out of their + * SRCU read-side critical sections, then loop waiting 1/HZ + * seconds per iteration. */ + if (srcu_readers_active_idx(sp, idx)) + udelay(CONFIG_SRCU_SYNCHRONIZE_DELAY); while (srcu_readers_active_idx(sp, idx)) schedule_timeout_interruptible(1); |