From ddc465936643108d5ba61f88594a2868d6a156ab Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Jonathan=20Neusch=C3=A4fer?= Date: Thu, 5 Mar 2020 23:22:55 +0100 Subject: Revert "rculist: Describe variadic macro argument in a Sphinx-compatible way" MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This reverts commit f452ee096d95482892b101bde4fd037fa025d3cc. The workaround became unnecessary with commit 43756e347f21 ("scripts/kernel-doc: Add support for named variable macro arguments"). Signed-off-by: Jonathan Neuschäfer Signed-off-by: Paul E. McKenney --- include/linux/rculist.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 8214cdc715f2..7375bb3da140 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -371,7 +371,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, * @pos: the type * to use as a loop cursor. * @head: the head for your list. * @member: the name of the list_head within the struct. - * @cond...: optional lockdep expression if called from non-RCU protection. + * @cond: optional lockdep expression if called from non-RCU protection. * * This list-traversal primitive may safely run concurrently with * the _rcu list-mutation primitives such as list_add_rcu() @@ -646,7 +646,7 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n, * @pos: the type * to use as a loop cursor. * @head: the head for your list. * @member: the name of the hlist_node within the struct. - * @cond...: optional lockdep expression if called from non-RCU protection. + * @cond: optional lockdep expression if called from non-RCU protection. * * This list-traversal primitive may safely run concurrently with * the _rcu list-mutation primitives such as hlist_add_head_rcu() -- cgit v1.2.3 From 6be7436d2245d3dd8b9a8f949367c13841c23308 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 10 Apr 2020 13:47:41 -0700 Subject: rcu: Add rcu_gp_might_be_stalled() This commit adds rcu_gp_might_be_stalled(), which returns true if there is some reason to believe that the RCU grace period is stalled. The use case is where an RCU free-memory path needs to allocate memory in order to free it, a situation that should be avoided where possible. But where it is necessary, there is always the alternative of using synchronize_rcu() to wait for a grace period in order to avoid the allocation. And if the grace period is stalled, allocating memory to asynchronously wait for it is a bad idea of epic proportions: Far better to let others use the memory, because these others might actually be able to free that memory before the grace period ends. Thus, rcu_gp_might_be_stalled() can be used to help decide whether allocating memory on an RCU free path is a semi-reasonable course of action. Cc: Joel Fernandes Cc: Uladzislau Rezki Signed-off-by: Paul E. McKenney --- include/linux/rcutiny.h | 1 + include/linux/rcutree.h | 1 + 2 files changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 045c28b71f4f..dbf5ac439594 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -87,6 +87,7 @@ static inline bool rcu_inkernel_boot_has_ended(void) { return true; } static inline bool rcu_is_watching(void) { return true; } static inline void rcu_momentary_dyntick_idle(void) { } static inline void kfree_rcu_scheduler_running(void) { } +static inline bool rcu_gp_might_be_stalled(void) { return false; } /* Avoid RCU read-side critical sections leaking across. */ static inline void rcu_all_qs(void) { barrier(); } diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 45f3f66bb04d..fbc26274af4d 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -39,6 +39,7 @@ void rcu_barrier(void); bool rcu_eqs_special_set(int cpu); void rcu_momentary_dyntick_idle(void); void kfree_rcu_scheduler_running(void); +bool rcu_gp_might_be_stalled(void); unsigned long get_state_synchronize_rcu(void); void cond_synchronize_rcu(unsigned long oldstate); -- cgit v1.2.3 From f0bdf6d473cf12a488a78422e15aafdfe77cf853 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Sat, 15 Feb 2020 14:52:32 -0800 Subject: rcu: Remove unused ->rcu_read_unlock_special.b.deferred_qs field The ->rcu_read_unlock_special.b.deferred_qs field is set to true in rcu_read_unlock_special() but never set to false. This is not particularly useful, so this commit removes this field. The only possible justification for this field is to ease debugging of RCU deferred quiscent states, but the combination of the other ->rcu_read_unlock_special fields plus ->rcu_blocked_node and of course ->rcu_read_lock_nesting should cover debugging needs. And if this last proves incorrect, this patch can always be reverted, along with the required setting of ->rcu_read_unlock_special.b.deferred_qs to false in rcu_preempt_deferred_qs_irqrestore(). Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney --- include/linux/sched.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/sched.h b/include/linux/sched.h index 4418f5cb8324..a4b727f57095 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -613,7 +613,7 @@ union rcu_special { u8 blocked; u8 need_qs; u8 exp_hint; /* Hint for performance. */ - u8 deferred_qs; + u8 pad; /* No garbage from compiler! */ } b; /* Bits. */ u32 s; /* Set of bits. */ }; -- cgit v1.2.3 From 2beaf3280e57bb891f8012dca49c87ed0f01e2f3 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Mar 2020 14:23:21 -0700 Subject: sched/core: Add function to sample state of locked-down task A running task's state can be sampled in a consistent manner (for example, for diagnostic purposes) simply by invoking smp_call_function_single() on its CPU, which may be obtained using task_cpu(), then having the IPI handler verify that the desired task is in fact still running. However, if the task is not running, this sampling can in theory be done immediately and directly. In practice, the task might start running at any time, including during the sampling period. Gaining a consistent sample of a not-running task therefore requires that something be done to lock down the target task's state. This commit therefore adds a try_invoke_on_locked_down_task() function that invokes a specified function if the specified task can be locked down, returning true if successful and if the specified function returns true. Otherwise this function simply returns false. Given that the function passed to try_invoke_on_nonrunning_task() might be invoked with a runqueue lock held, that function had better be quite lightweight. The function is passed the target task's task_struct pointer and the argument passed to try_invoke_on_locked_down_task(), allowing easy access to task state and to a location for further variables to be passed in and out. Note that the specified function will be called even if the specified task is currently running. The function can use ->on_rq and task_curr() to quickly and easily determine the task's state, and can return false if this state is not to the function's liking. The caller of the try_invoke_on_locked_down_task() would then see the false return value, and could take appropriate action, for example, trying again later or sending an IPI if matters are more urgent. It is expected that use cases such as the RCU CPU stall warning code will simply return false if the task is currently running. However, there are use cases involving nohz_full CPUs where the specified function might instead fall back to an alternative sampling scheme that relies on heavier synchronization (such as memory barriers) in the target task. Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Ben Segall Cc: Mel Gorman [ paulmck: Apply feedback from Peter Zijlstra and Steven Rostedt. ] [ paulmck: Invoke if running to handle feedback from Mathieu Desnoyers. ] Reviewed-by: Steven Rostedt (VMware) Reviewed-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- include/linux/wait.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/wait.h b/include/linux/wait.h index feeb6be5cad6..898c890fc153 100644 --- a/include/linux/wait.h +++ b/include/linux/wait.h @@ -1149,4 +1149,6 @@ int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, i (wait)->flags = 0; \ } while (0) +bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg); + #endif /* _LINUX_WAIT_H */ -- cgit v1.2.3 From b3d73156b075014ce5b2609f4f47723d6c0c23d6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 6 Mar 2020 13:58:27 -0800 Subject: rcu: Reinstate synchronize_rcu_mult() With the advent and likely usage of synchronize_rcu_rude(), there is again a need to wait on multiple types of RCU grace periods, for example, call_rcu_tasks() and call_rcu_tasks_rude(). This commit therefore reinstates synchronize_rcu_mult() in order to allow these grace periods to be straightforwardly waited on concurrently. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate_wait.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'include/linux') diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h index c0578ba23c1a..699b938358bf 100644 --- a/include/linux/rcupdate_wait.h +++ b/include/linux/rcupdate_wait.h @@ -31,4 +31,23 @@ do { \ #define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__) +/** + * synchronize_rcu_mult - Wait concurrently for multiple grace periods + * @...: List of call_rcu() functions for different grace periods to wait on + * + * This macro waits concurrently for multiple types of RCU grace periods. + * For example, synchronize_rcu_mult(call_rcu, call_rcu_tasks) would wait + * on concurrent RCU and RCU-tasks grace periods. Waiting on a given SRCU + * domain requires you to write a wrapper function for that SRCU domain's + * call_srcu() function, with this wrapper supplying the pointer to the + * corresponding srcu_struct. + * + * The first argument tells Tiny RCU's _wait_rcu_gp() not to + * bother waiting for RCU. The reason for this is because anywhere + * synchronize_rcu_mult() can be called is automatically already a full + * grace period. + */ +#define synchronize_rcu_mult(...) \ + _wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__) + #endif /* _LINUX_SCHED_RCUPDATE_WAIT_H */ -- cgit v1.2.3 From 5873b8a94e5dae04b8e11fc798df512614e6d1e7 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 3 Mar 2020 11:49:21 -0800 Subject: rcu-tasks: Refactor RCU-tasks to allow variants to be added This commit splits out generic processing from RCU-tasks-specific processing in order to allow additional flavors to be added. It also adds a def_bool TASKS_RCU_GENERIC to enable the common RCU-tasks infrastructure code. This is primarily, but not entirely, a code-movement commit. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'include/linux') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 2678a37c3169..5523145e0a78 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -129,7 +129,7 @@ static inline void rcu_init_nohz(void) { } * Note a quasi-voluntary context switch for RCU-tasks's benefit. * This is a macro rather than an inline function to avoid #include hell. */ -#ifdef CONFIG_TASKS_RCU +#ifdef CONFIG_TASKS_RCU_GENERIC #define rcu_tasks_qs(t) \ do { \ if (READ_ONCE((t)->rcu_tasks_holdout)) \ @@ -140,14 +140,14 @@ void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); void synchronize_rcu_tasks(void); void exit_tasks_rcu_start(void); void exit_tasks_rcu_finish(void); -#else /* #ifdef CONFIG_TASKS_RCU */ +#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ #define rcu_tasks_qs(t) do { } while (0) #define rcu_note_voluntary_context_switch(t) do { } while (0) #define call_rcu_tasks call_rcu #define synchronize_rcu_tasks synchronize_rcu static inline void exit_tasks_rcu_start(void) { } static inline void exit_tasks_rcu_finish(void) { } -#endif /* #else #ifdef CONFIG_TASKS_RCU */ +#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ /** * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU -- cgit v1.2.3 From c84aad765406c4c7573ce449e8a9977ebb8f4cb9 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 2 Mar 2020 21:06:43 -0800 Subject: rcu-tasks: Add an RCU-tasks rude variant This commit adds a "rude" variant of RCU-tasks that has as quiescent states schedule(), cond_resched_tasks_rcu_qs(), userspace execution, and (in theory, anyway) cond_resched(). In other words, RCU-tasks rude readers are regions of code with preemption disabled, but excluding code early in the CPU-online sequence and late in the CPU-offline sequence. Updates make use of IPIs and force an IPI and a context switch on each online CPU. This variant is useful in some situations in tracing. Suggested-by: Steven Rostedt [ paulmck: Apply EXPORT_SYMBOL_GPL() feedback from Qiujun Huang. ] Signed-off-by: Paul E. McKenney [ paulmck: Apply review feedback from Steve Rostedt. ] --- include/linux/rcupdate.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/linux') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 5523145e0a78..2be97a83f266 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -37,6 +37,7 @@ /* Exported common interfaces */ void call_rcu(struct rcu_head *head, rcu_callback_t func); void rcu_barrier_tasks(void); +void rcu_barrier_tasks_rude(void); void synchronize_rcu(void); #ifdef CONFIG_PREEMPT_RCU @@ -138,6 +139,8 @@ static inline void rcu_init_nohz(void) { } #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t) void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); void synchronize_rcu_tasks(void); +void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); +void synchronize_rcu_tasks_rude(void); void exit_tasks_rcu_start(void); void exit_tasks_rcu_finish(void); #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ -- cgit v1.2.3 From d5f177d35c24429c87db2567d20563fc16f7e8f6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 9 Mar 2020 19:56:53 -0700 Subject: rcu-tasks: Add an RCU Tasks Trace to simplify protection of tracing hooks Because RCU does not watch exception early-entry/late-exit, idle-loop, or CPU-hotplug execution, protection of tracing and BPF operations is needlessly complicated. This commit therefore adds a variant of Tasks RCU that: o Has explicit read-side markers to allow finite grace periods in the face of in-kernel loops for PREEMPT=n builds. These markers are rcu_read_lock_trace() and rcu_read_unlock_trace(). o Protects code in the idle loop, exception entry/exit, and CPU-hotplug code paths. In this respect, RCU-tasks trace is similar to SRCU, but with lighter-weight readers. o Avoids expensive read-side instruction, having overhead similar to that of Preemptible RCU. There are of course downsides: o The grace-period code can send IPIs to CPUs, even when those CPUs are in the idle loop or in nohz_full userspace. This is mitigated by later commits. o It is necessary to scan the full tasklist, much as for Tasks RCU. o There is a single callback queue guarded by a single lock, again, much as for Tasks RCU. However, those early use cases that request multiple grace periods in quick succession are expected to do so from a single task, which makes the single lock almost irrelevant. If needed, multiple callback queues can be provided using any number of schemes. Perhaps most important, this variant of RCU does not affect the vanilla flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace readers can operate from idle, offline, and exception entry/exit in no way enables rcu_preempt and rcu_sched readers to do so. The memory ordering was outlined here: https://lore.kernel.org/lkml/20200319034030.GX3199@paulmck-ThinkPad-P72/ This effort benefited greatly from off-list discussions of BPF requirements with Alexei Starovoitov and Andrii Nakryiko. At least some of the on-list discussions are captured in the Link: tags below. In addition, KCSAN was quite helpful in finding some early bugs. Link: https://lore.kernel.org/lkml/20200219150744.428764577@infradead.org/ Link: https://lore.kernel.org/lkml/87mu8p797b.fsf@nanos.tec.linutronix.de/ Link: https://lore.kernel.org/lkml/20200225221305.605144982@linutronix.de/ Cc: Alexei Starovoitov Cc: Andrii Nakryiko [ paulmck: Apply feedback from Steve Rostedt and Joel Fernandes. ] [ paulmck: Decrement trc_n_readers_need_end upon IPI failure. ] [ paulmck: Fix locking issue reported by rcutorture. ] Signed-off-by: Paul E. McKenney --- include/linux/rcupdate_trace.h | 84 ++++++++++++++++++++++++++++++++++++++++++ include/linux/sched.h | 8 ++++ 2 files changed, 92 insertions(+) create mode 100644 include/linux/rcupdate_trace.h (limited to 'include/linux') diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h new file mode 100644 index 000000000000..ed97e10817bd --- /dev/null +++ b/include/linux/rcupdate_trace.h @@ -0,0 +1,84 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Read-Copy Update mechanism for mutual exclusion, adapted for tracing. + * + * Copyright (C) 2020 Paul E. McKenney. + */ + +#ifndef __LINUX_RCUPDATE_TRACE_H +#define __LINUX_RCUPDATE_TRACE_H + +#include +#include + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + +extern struct lockdep_map rcu_trace_lock_map; + +static inline int rcu_read_lock_trace_held(void) +{ + return lock_is_held(&rcu_trace_lock_map); +} + +#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ + +static inline int rcu_read_lock_trace_held(void) +{ + return 1; +} + +#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ + +#ifdef CONFIG_TASKS_TRACE_RCU + +void rcu_read_unlock_trace_special(struct task_struct *t); + +/** + * rcu_read_lock_trace - mark beginning of RCU-trace read-side critical section + * + * When synchronize_rcu_trace() is invoked by one task, then that task + * is guaranteed to block until all other tasks exit their read-side + * critical sections. Similarly, if call_rcu_trace() is invoked on one + * task while other tasks are within RCU read-side critical sections, + * invocation of the corresponding RCU callback is deferred until after + * the all the other tasks exit their critical sections. + * + * For more details, please see the documentation for rcu_read_lock(). + */ +static inline void rcu_read_lock_trace(void) +{ + struct task_struct *t = current; + + WRITE_ONCE(t->trc_reader_nesting, READ_ONCE(t->trc_reader_nesting) + 1); + rcu_lock_acquire(&rcu_trace_lock_map); +} + +/** + * rcu_read_unlock_trace - mark end of RCU-trace read-side critical section + * + * Pairs with a preceding call to rcu_read_lock_trace(), and nesting is + * allowed. Invoking a rcu_read_unlock_trace() when there is no matching + * rcu_read_lock_trace() is verboten, and will result in lockdep complaints. + * + * For more details, please see the documentation for rcu_read_unlock(). + */ +static inline void rcu_read_unlock_trace(void) +{ + int nesting; + struct task_struct *t = current; + + rcu_lock_release(&rcu_trace_lock_map); + nesting = READ_ONCE(t->trc_reader_nesting) - 1; + WRITE_ONCE(t->trc_reader_nesting, nesting); + if (likely(!READ_ONCE(t->trc_reader_need_end)) || nesting) + return; // We assume shallow reader nesting. + rcu_read_unlock_trace_special(t); +} + +void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); +void synchronize_rcu_tasks_trace(void); +void rcu_barrier_tasks_trace(void); + +#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ + +#endif /* __LINUX_RCUPDATE_TRACE_H */ diff --git a/include/linux/sched.h b/include/linux/sched.h index a4b727f57095..864f60e51c41 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -724,6 +724,14 @@ struct task_struct { struct list_head rcu_tasks_holdout_list; #endif /* #ifdef CONFIG_TASKS_RCU */ +#ifdef CONFIG_TASKS_TRACE_RCU + int trc_reader_nesting; + int trc_ipi_to_cpu; + bool trc_reader_need_end; + bool trc_reader_checked; + struct list_head trc_holdout_list; +#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ + struct sched_info sched_info; struct list_head tasks; -- cgit v1.2.3 From 43766c3eadcf6033c92eb953f88801aebac0f785 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 16 Mar 2020 20:38:29 -0700 Subject: rcu-tasks: Make RCU Tasks Trace make use of RCU scheduler hooks This commit makes the calls to rcu_tasks_qs() detect and report quiescent states for RCU tasks trace. If the task is in a quiescent state and if ->trc_reader_checked is not yet set, the task sets its own ->trc_reader_checked. This will cause the grace-period kthread to remove it from the holdout list if it still remains there. [ paulmck: Fix conditional compilation per kbuild test robot feedback. ] Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 44 +++++++++++++++++++++++++++++++++++++------- include/linux/rcutiny.h | 2 +- 2 files changed, 38 insertions(+), 8 deletions(-) (limited to 'include/linux') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 2be97a83f266..659cbfa7581a 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -131,20 +131,50 @@ static inline void rcu_init_nohz(void) { } * This is a macro rather than an inline function to avoid #include hell. */ #ifdef CONFIG_TASKS_RCU_GENERIC -#define rcu_tasks_qs(t) \ - do { \ - if (READ_ONCE((t)->rcu_tasks_holdout)) \ - WRITE_ONCE((t)->rcu_tasks_holdout, false); \ + +# ifdef CONFIG_TASKS_RCU +# define rcu_tasks_classic_qs(t, preempt) \ + do { \ + if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \ + WRITE_ONCE((t)->rcu_tasks_holdout, false); \ } while (0) -#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t) void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); void synchronize_rcu_tasks(void); +# else +# define rcu_tasks_classic_qs(t, preempt) do { } while (0) +# define call_rcu_tasks call_rcu +# define synchronize_rcu_tasks synchronize_rcu +# endif + +# ifdef CONFIG_TASKS_RCU_TRACE +# define rcu_tasks_trace_qs(t) \ + do { \ + if (!likely(READ_ONCE((t)->trc_reader_checked)) && \ + !unlikely(READ_ONCE((t)->trc_reader_nesting))) { \ + smp_store_release(&(t)->trc_reader_checked, true); \ + smp_mb(); /* Readers partitioned by store. */ \ + } \ + } while (0) +# else +# define rcu_tasks_trace_qs(t) do { } while (0) +# endif + +#define rcu_tasks_qs(t, preempt) \ +do { \ + rcu_tasks_classic_qs((t), (preempt)); \ + rcu_tasks_trace_qs((t)); \ +} while (0) + +# ifdef CONFIG_TASKS_RUDE_RCU void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); void synchronize_rcu_tasks_rude(void); +# endif + +#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false) void exit_tasks_rcu_start(void); void exit_tasks_rcu_finish(void); #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ -#define rcu_tasks_qs(t) do { } while (0) +#define rcu_tasks_qs(t, preempt) do { } while (0) #define rcu_note_voluntary_context_switch(t) do { } while (0) #define call_rcu_tasks call_rcu #define synchronize_rcu_tasks synchronize_rcu @@ -161,7 +191,7 @@ static inline void exit_tasks_rcu_finish(void) { } */ #define cond_resched_tasks_rcu_qs() \ do { \ - rcu_tasks_qs(current); \ + rcu_tasks_qs(current, false); \ cond_resched(); \ } while (0) diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 045c28b71f4f..d77e11186afd 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -49,7 +49,7 @@ static inline void rcu_softirq_qs(void) #define rcu_note_context_switch(preempt) \ do { \ rcu_qs(); \ - rcu_tasks_qs(current); \ + rcu_tasks_qs(current, (preempt)); \ } while (0) static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt) -- cgit v1.2.3 From 276c410448dbca357a2bc3539acfe04862e5f172 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 17 Mar 2020 16:02:06 -0700 Subject: rcu-tasks: Split ->trc_reader_need_end This commit splits ->trc_reader_need_end by using the rcu_special union. This change permits readers to check to see if a memory barrier is required without any added overhead in the common case where no such barrier is required. This commit also adds the read-side checking. Later commits will add the machinery to properly set the new ->trc_reader_special.b.need_mb field. This commit also makes rcu_read_unlock_trace_special() tolerate nested read-side critical sections within interrupt and NMI handlers. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate_trace.h | 11 +++++++---- include/linux/sched.h | 4 ++-- 2 files changed, 9 insertions(+), 6 deletions(-) (limited to 'include/linux') diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h index ed97e10817bd..c42b365ca176 100644 --- a/include/linux/rcupdate_trace.h +++ b/include/linux/rcupdate_trace.h @@ -31,7 +31,7 @@ static inline int rcu_read_lock_trace_held(void) #ifdef CONFIG_TASKS_TRACE_RCU -void rcu_read_unlock_trace_special(struct task_struct *t); +void rcu_read_unlock_trace_special(struct task_struct *t, int nesting); /** * rcu_read_lock_trace - mark beginning of RCU-trace read-side critical section @@ -50,6 +50,8 @@ static inline void rcu_read_lock_trace(void) struct task_struct *t = current; WRITE_ONCE(t->trc_reader_nesting, READ_ONCE(t->trc_reader_nesting) + 1); + if (t->trc_reader_special.b.need_mb) + smp_mb(); // Pairs with update-side barriers rcu_lock_acquire(&rcu_trace_lock_map); } @@ -69,10 +71,11 @@ static inline void rcu_read_unlock_trace(void) rcu_lock_release(&rcu_trace_lock_map); nesting = READ_ONCE(t->trc_reader_nesting) - 1; - WRITE_ONCE(t->trc_reader_nesting, nesting); - if (likely(!READ_ONCE(t->trc_reader_need_end)) || nesting) + if (likely(!READ_ONCE(t->trc_reader_special.s)) || nesting) { + WRITE_ONCE(t->trc_reader_nesting, nesting); return; // We assume shallow reader nesting. - rcu_read_unlock_trace_special(t); + } + rcu_read_unlock_trace_special(t, nesting); } void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); diff --git a/include/linux/sched.h b/include/linux/sched.h index 864f60e51c41..9437b53cc603 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -613,7 +613,7 @@ union rcu_special { u8 blocked; u8 need_qs; u8 exp_hint; /* Hint for performance. */ - u8 pad; /* No garbage from compiler! */ + u8 need_mb; /* Readers need smp_mb(). */ } b; /* Bits. */ u32 s; /* Set of bits. */ }; @@ -727,7 +727,7 @@ struct task_struct { #ifdef CONFIG_TASKS_TRACE_RCU int trc_reader_nesting; int trc_ipi_to_cpu; - bool trc_reader_need_end; + union rcu_special trc_reader_special; bool trc_reader_checked; struct list_head trc_holdout_list; #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ -- cgit v1.2.3 From 9ae58d7bd11f1fc4c96389df11751f8593d8bd33 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 18 Mar 2020 17:16:37 -0700 Subject: rcu-tasks: Add Kconfig option to mediate smp_mb() vs. IPI This commit provides a new TASKS_TRACE_RCU_READ_MB Kconfig option that enables use of read-side memory barriers by both rcu_read_lock_trace() and rcu_read_unlock_trace() when the are executed with the current->trc_reader_special.b.need_mb flag set. This flag is currently never set. Doing that is the subject of a later commit. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate_trace.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h index c42b365ca176..4c25a41f8b27 100644 --- a/include/linux/rcupdate_trace.h +++ b/include/linux/rcupdate_trace.h @@ -50,7 +50,8 @@ static inline void rcu_read_lock_trace(void) struct task_struct *t = current; WRITE_ONCE(t->trc_reader_nesting, READ_ONCE(t->trc_reader_nesting) + 1); - if (t->trc_reader_special.b.need_mb) + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && + t->trc_reader_special.b.need_mb) smp_mb(); // Pairs with update-side barriers rcu_lock_acquire(&rcu_trace_lock_map); } -- cgit v1.2.3 From be44ae62431196ac2a55198c0855028fff3ccfb4 Mon Sep 17 00:00:00 2001 From: Randy Dunlap Date: Tue, 25 Feb 2020 21:09:19 -0800 Subject: locktorture.c: Fix if-statement empty body warnings MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When using -Wextra, gcc complains about torture_preempt_schedule() when its definition is empty (i.e., when CONFIG_PREEMPTION is not set/enabled). Fix these warnings by adding an empty do-while block for that macro when CONFIG_PREEMPTION is not set. Fixes these build warnings: ../kernel/locking/locktorture.c:119:29: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body] ../kernel/locking/locktorture.c:166:29: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body] ../kernel/locking/locktorture.c:337:29: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body] ../kernel/locking/locktorture.c:490:29: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body] ../kernel/locking/locktorture.c:528:29: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body] ../kernel/locking/locktorture.c:553:29: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body] I have verified that there is no object code change (with gcc 7.5.0). Signed-off-by: Randy Dunlap Cc: Davidlohr Bueso Cc: Josh Triplett Signed-off-by: "Paul E. McKenney" --- include/linux/torture.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/torture.h b/include/linux/torture.h index 6241f59e2d6f..629b66e6c161 100644 --- a/include/linux/torture.h +++ b/include/linux/torture.h @@ -89,7 +89,7 @@ void _torture_stop_kthread(char *m, struct task_struct **tp); #ifdef CONFIG_PREEMPTION #define torture_preempt_schedule() preempt_schedule() #else -#define torture_preempt_schedule() +#define torture_preempt_schedule() do { } while (0) #endif #endif /* __LINUX_TORTURE_H */ -- cgit v1.2.3 From 69ea03b56ed2c7189ccd0b5910ad39f3cad1df21 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 19 Feb 2020 09:46:47 +0100 Subject: hardirq/nmi: Allow nested nmi_enter() Since there are already a number of sites (ARM64, PowerPC) that effectively nest nmi_enter(), make the primitive support this before adding even more. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Acked-by: Marc Zyngier Acked-by: Will Deacon Cc: Michael Ellerman Link: https://lkml.kernel.org/r/20200505134100.864179229@linutronix.de --- include/linux/hardirq.h | 5 ++++- include/linux/preempt.h | 4 ++-- 2 files changed, 6 insertions(+), 3 deletions(-) (limited to 'include/linux') diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index 7c8b82f69288..a043ad826c67 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -65,13 +65,16 @@ extern void irq_exit(void); #define arch_nmi_exit() do { } while (0) #endif +/* + * nmi_enter() can nest up to 15 times; see NMI_BITS. + */ #define nmi_enter() \ do { \ arch_nmi_enter(); \ printk_nmi_enter(); \ lockdep_off(); \ ftrace_nmi_enter(); \ - BUG_ON(in_nmi()); \ + BUG_ON(in_nmi() == NMI_MASK); \ preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \ rcu_nmi_enter(); \ lockdep_hardirq_enter(); \ diff --git a/include/linux/preempt.h b/include/linux/preempt.h index bc3f1aecaa19..7d9c1c0e149c 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -26,13 +26,13 @@ * PREEMPT_MASK: 0x000000ff * SOFTIRQ_MASK: 0x0000ff00 * HARDIRQ_MASK: 0x000f0000 - * NMI_MASK: 0x00100000 + * NMI_MASK: 0x00f00000 * PREEMPT_NEED_RESCHED: 0x80000000 */ #define PREEMPT_BITS 8 #define SOFTIRQ_BITS 8 #define HARDIRQ_BITS 4 -#define NMI_BITS 1 +#define NMI_BITS 4 #define PREEMPT_SHIFT 0 #define SOFTIRQ_SHIFT (PREEMPT_SHIFT + PREEMPT_BITS) -- cgit v1.2.3 From e616cb8daadf637175af4fe53138a94c190c4816 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 24 Feb 2020 22:14:51 +0100 Subject: lockdep: Always inline lockdep_{off,on}() These functions are called {early,late} in nmi_{enter,exit} and should not be traced or probed. They are also puny, so 'inline' them. Reported-by: Steven Rostedt Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Reviewed-by: Alexandre Chartre Link: https://lkml.kernel.org/r/20200505134101.048523500@linutronix.de --- include/linux/lockdep.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 206774ac6946..8fce5c98a4b0 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -308,8 +308,27 @@ extern void lockdep_set_selftest_task(struct task_struct *task); extern void lockdep_init_task(struct task_struct *task); -extern void lockdep_off(void); -extern void lockdep_on(void); +/* + * Split the recrursion counter in two to readily detect 'off' vs recursion. + */ +#define LOCKDEP_RECURSION_BITS 16 +#define LOCKDEP_OFF (1U << LOCKDEP_RECURSION_BITS) +#define LOCKDEP_RECURSION_MASK (LOCKDEP_OFF - 1) + +/* + * lockdep_{off,on}() are macros to avoid tracing and kprobes; not inlines due + * to header dependencies. + */ + +#define lockdep_off() \ +do { \ + current->lockdep_recursion += LOCKDEP_OFF; \ +} while (0) + +#define lockdep_on() \ +do { \ + current->lockdep_recursion -= LOCKDEP_OFF; \ +} while (0) extern void lockdep_register_key(struct lock_class_key *key); extern void lockdep_unregister_key(struct lock_class_key *key); -- cgit v1.2.3 From 178ba00c354eb15cec6806a812771e60a5ae3ea1 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 24 Feb 2020 22:26:21 +0100 Subject: sh/ftrace: Move arch_ftrace_nmi_{enter,exit} into nmi exception SuperH is the last remaining user of arch_ftrace_nmi_{enter,exit}(), remove it from the generic code and into the SuperH code. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Reviewed-by: Alexandre Chartre Acked-by: Steven Rostedt (VMware) Cc: Rich Felker Cc: Yoshinori Sato Link: https://lkml.kernel.org/r/20200505134101.248881738@linutronix.de --- include/linux/ftrace_irq.h | 11 ----------- 1 file changed, 11 deletions(-) (limited to 'include/linux') diff --git a/include/linux/ftrace_irq.h b/include/linux/ftrace_irq.h index ccda97dc7f8b..0abd9a1d2852 100644 --- a/include/linux/ftrace_irq.h +++ b/include/linux/ftrace_irq.h @@ -2,15 +2,6 @@ #ifndef _LINUX_FTRACE_IRQ_H #define _LINUX_FTRACE_IRQ_H - -#ifdef CONFIG_FTRACE_NMI_ENTER -extern void arch_ftrace_nmi_enter(void); -extern void arch_ftrace_nmi_exit(void); -#else -static inline void arch_ftrace_nmi_enter(void) { } -static inline void arch_ftrace_nmi_exit(void) { } -#endif - #ifdef CONFIG_HWLAT_TRACER extern bool trace_hwlat_callback_enabled; extern void trace_hwlat_callback(bool enter); @@ -22,12 +13,10 @@ static inline void ftrace_nmi_enter(void) if (trace_hwlat_callback_enabled) trace_hwlat_callback(true); #endif - arch_ftrace_nmi_enter(); } static inline void ftrace_nmi_exit(void) { - arch_ftrace_nmi_exit(); #ifdef CONFIG_HWLAT_TRACER if (trace_hwlat_callback_enabled) trace_hwlat_callback(false); -- cgit v1.2.3 From f93524eb9c54f49be150167918f6546b0a2e09b1 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 12 Feb 2020 21:01:16 +0100 Subject: sched,rcu,tracing: Avoid tracing before in_nmi() is correct If a tracer is invoked before in_nmi() becomes true, the tracer can no longer detect it is called from NMI context and behave correctly. Therefore change nmi_{enter,exit}() to use __preempt_count_{add,sub}() as the normal preempt_count_{add,sub}() have a (desired) function trace entry. This fixes a potential issue with the current code; when the function-tracer has stack-tracing enabled __trace_stack() will malfunction when it hits the preempt_count_add() function entry from NMI context. Suggested-by: Steven Rostedt (VMware) Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Reviewed-by: Steven Rostedt (VMware) Reviewed-by: Alexandre Chartre Link: https://lkml.kernel.org/r/20200505134101.434193525@linutronix.de --- include/linux/hardirq.h | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index a043ad826c67..621556efe45f 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -65,6 +65,15 @@ extern void irq_exit(void); #define arch_nmi_exit() do { } while (0) #endif +/* + * NMI vs Tracing + * -------------- + * + * We must not land in a tracer until (or after) we've changed preempt_count + * such that in_nmi() becomes true. To that effect all NMI C entry points must + * be marked 'notrace' and call nmi_enter() as soon as possible. + */ + /* * nmi_enter() can nest up to 15 times; see NMI_BITS. */ @@ -75,7 +84,7 @@ extern void irq_exit(void); lockdep_off(); \ ftrace_nmi_enter(); \ BUG_ON(in_nmi() == NMI_MASK); \ - preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \ + __preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \ rcu_nmi_enter(); \ lockdep_hardirq_enter(); \ } while (0) @@ -85,7 +94,7 @@ extern void irq_exit(void); lockdep_hardirq_exit(); \ rcu_nmi_exit(); \ BUG_ON(!in_nmi()); \ - preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \ + __preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \ ftrace_nmi_exit(); \ lockdep_on(); \ printk_nmi_exit(); \ -- cgit v1.2.3 From 5567d11c21a1d508a91a8cb64a819783a0835d9f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 19 Feb 2020 10:22:06 +0100 Subject: x86/mce: Send #MC singal from task work Convert #MC over to using task_work_add(); it will run the same code slightly later, on the return to user path of the same exception. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Reviewed-by: Alexandre Chartre Link: https://lkml.kernel.org/r/20200505134100.957390899@linutronix.de --- include/linux/sched.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include/linux') diff --git a/include/linux/sched.h b/include/linux/sched.h index 9437b53cc603..57d0ed061ae4 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1297,6 +1297,12 @@ struct task_struct { unsigned long prev_lowest_stack; #endif +#ifdef CONFIG_X86_MCE + u64 mce_addr; + u64 mce_status; + struct callback_head mce_kill_me; +#endif + /* * New fields for task_struct should be added above here, so that * they are included in the randomized portion of task_struct. -- cgit v1.2.3 From 8ae0ae6737ad449c8ae21e2bb01d9736f360a933 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sun, 3 May 2020 15:08:52 +0200 Subject: rcu: Provide rcu_irq_exit_preempt() Interrupts and exceptions invoke rcu_irq_enter() on entry and need to invoke rcu_irq_exit() before they either return to the interrupted code or invoke the scheduler due to preemption. The general assumption is that RCU idle code has to have preemption disabled so that a return from interrupt cannot schedule. So the return from interrupt code invokes rcu_irq_exit() and preempt_schedule_irq(). If there is any imbalance in the rcu_irq/nmi* invocations or RCU idle code had preemption enabled then this goes unnoticed until the CPU goes idle or some other RCU check is executed. Provide rcu_irq_exit_preempt() which can be invoked from the interrupt/exception return code in case that preemption is enabled. It invokes rcu_irq_exit() and contains a few sanity checks in case that CONFIG_PROVE_RCU is enabled to catch such issues directly. Signed-off-by: Thomas Gleixner Reviewed-by: Paul E. McKenney Reviewed-by: Alexandre Chartre Acked-by: Peter Zijlstra Link: https://lkml.kernel.org/r/20200505134904.364456424@linutronix.de --- include/linux/rcutiny.h | 1 + include/linux/rcutree.h | 1 + 2 files changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 3465ba704a11..980eb78751d9 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -71,6 +71,7 @@ static inline void rcu_irq_enter(void) { } static inline void rcu_irq_exit_irqson(void) { } static inline void rcu_irq_enter_irqson(void) { } static inline void rcu_irq_exit(void) { } +static inline void rcu_irq_exit_preempt(void) { } static inline void exit_rcu(void) { } static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t) { diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index fbc26274af4d..02016e0aa8eb 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -47,6 +47,7 @@ void rcu_idle_enter(void); void rcu_idle_exit(void); void rcu_irq_enter(void); void rcu_irq_exit(void); +void rcu_irq_exit_preempt(void); void rcu_irq_enter_irqson(void); void rcu_irq_exit_irqson(void); -- cgit v1.2.3 From b1fcf9b83c4149c63d1e0c699e85f93cbe28e211 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 12 May 2020 09:44:43 +0200 Subject: rcu: Provide __rcu_is_watching() Same as rcu_is_watching() but without the preempt_disable/enable() pair inside the function. It is merked noinstr so it ends up in the non-instrumentable text section. This is useful for non-preemptible code especially in the low level entry section. Using rcu_is_watching() there results in a call to the preempt_schedule_notrace() thunk which triggers noinstr section warnings in objtool. Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Link: https://lkml.kernel.org/r/20200512213810.518709291@linutronix.de --- include/linux/rcutiny.h | 1 + include/linux/rcutree.h | 1 + 2 files changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 980eb78751d9..c869fb20cc51 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -86,6 +86,7 @@ static inline void rcu_scheduler_starting(void) { } static inline void rcu_end_inkernel_boot(void) { } static inline bool rcu_inkernel_boot_has_ended(void) { return true; } static inline bool rcu_is_watching(void) { return true; } +static inline bool __rcu_is_watching(void) { return true; } static inline void rcu_momentary_dyntick_idle(void) { } static inline void kfree_rcu_scheduler_running(void) { } static inline bool rcu_gp_might_be_stalled(void) { return false; } diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 02016e0aa8eb..9366fa4d0717 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -58,6 +58,7 @@ extern int rcu_scheduler_active __read_mostly; void rcu_end_inkernel_boot(void); bool rcu_inkernel_boot_has_ended(void); bool rcu_is_watching(void); +bool __rcu_is_watching(void); #ifndef CONFIG_PREEMPTION void rcu_all_qs(void); #endif -- cgit v1.2.3 From aaf2bc50df1f4bfc6857fc601fc7b21d5a18c6a1 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 21 May 2020 22:05:15 +0200 Subject: rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter() There will likely be exception handlers that can sleep, which rules out the usual approach of invoking rcu_nmi_enter() on entry and also rcu_nmi_exit() on all exit paths. However, the alternative approach of just not calling anything can prevent RCU from coaxing quiescent states from nohz_full CPUs that are looping in the kernel: RCU must instead IPI them explicitly. It would be better to enable the scheduler tick on such CPUs to interact with RCU in a lighter-weight manner, and this enabling is one of the things that rcu_nmi_enter() currently does. What is needed is something that helps RCU coax quiescent states while not preventing subsequent sleeps. This commit therefore splits out the nohz_full scheduler-tick enabling from the rest of the rcu_nmi_enter() logic into a new function named rcu_irq_enter_check_tick(). [ tglx: Renamed the function and made it a nop when context tracking is off ] [ mingo: Fixed a CONFIG_NO_HZ_FULL assumption, harmonized and fixed all the comment blocks and cleaned up rcu_nmi_enter()/exit() definitions. ] Suggested-by: Andy Lutomirski Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20200521202116.996113173@linutronix.de --- include/linux/hardirq.h | 29 +++++++++++++++++------------ 1 file changed, 17 insertions(+), 12 deletions(-) (limited to 'include/linux') diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index 621556efe45f..e07cf853aa16 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -2,31 +2,28 @@ #ifndef LINUX_HARDIRQ_H #define LINUX_HARDIRQ_H +#include #include #include #include #include #include - extern void synchronize_irq(unsigned int irq); extern bool synchronize_hardirq(unsigned int irq); -#if defined(CONFIG_TINY_RCU) - -static inline void rcu_nmi_enter(void) -{ -} +#ifdef CONFIG_NO_HZ_FULL +void __rcu_irq_enter_check_tick(void); +#else +static inline void __rcu_irq_enter_check_tick(void) { } +#endif -static inline void rcu_nmi_exit(void) +static __always_inline void rcu_irq_enter_check_tick(void) { + if (context_tracking_enabled()) + __rcu_irq_enter_check_tick(); } -#else -extern void rcu_nmi_enter(void); -extern void rcu_nmi_exit(void); -#endif - /* * It is safe to do non-atomic ops on ->hardirq_context, * because NMI handlers may not preempt and the ops are @@ -65,6 +62,14 @@ extern void irq_exit(void); #define arch_nmi_exit() do { } while (0) #endif +#ifdef CONFIG_TINY_RCU +static inline void rcu_nmi_enter(void) { } +static inline void rcu_nmi_exit(void) { } +#else +extern void rcu_nmi_enter(void); +extern void rcu_nmi_exit(void); +#endif + /* * NMI vs Tracing * -------------- -- cgit v1.2.3 From 07325d4a90d2d84de45cc07b134fd0f023dbb971 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 21 May 2020 22:05:16 +0200 Subject: rcu: Provide rcu_irq_exit_check_preempt() Provide a debug check which can be invoked from exception return to kernel mode before an attempt is made to schedule. Warn if RCU is not ready for this. Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar Cc: Paul E. McKenney Link: https://lore.kernel.org/r/20200521202117.089709607@linutronix.de --- include/linux/rcutiny.h | 1 + include/linux/rcutree.h | 6 ++++++ 2 files changed, 7 insertions(+) (limited to 'include/linux') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index c869fb20cc51..8512caeb7682 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -72,6 +72,7 @@ static inline void rcu_irq_exit_irqson(void) { } static inline void rcu_irq_enter_irqson(void) { } static inline void rcu_irq_exit(void) { } static inline void rcu_irq_exit_preempt(void) { } +static inline void rcu_irq_exit_check_preempt(void) { } static inline void exit_rcu(void) { } static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t) { diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 9366fa4d0717..d5cc9d675987 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -51,6 +51,12 @@ void rcu_irq_exit_preempt(void); void rcu_irq_enter_irqson(void); void rcu_irq_exit_irqson(void); +#ifdef CONFIG_PROVE_RCU +void rcu_irq_exit_check_preempt(void); +#else +static inline void rcu_irq_exit_check_preempt(void) { } +#endif + void exit_rcu(void); void rcu_scheduler_starting(void); -- cgit v1.2.3