From c71fd893f614f205dbc050d60299cc5496491c19 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Mon, 20 May 2019 16:59:00 -0400 Subject: locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER The owner field in the rw_semaphore structure is used primarily for optimistic spinning. However, identifying the rwsem owner can also be helpful in debugging as well as tracing locking related issues when analyzing crash dump. The owner field may also store state information that can be important to the operation of the rwsem. So the owner field is now made a permanent member of the rw_semaphore structure irrespective of CONFIG_RWSEM_SPIN_ON_OWNER. Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen Cc: Will Deacon Cc: huang ying Link: https://lkml.kernel.org/r/20190520205918.22251-2-longman@redhat.com Signed-off-by: Ingo Molnar --- include/linux/rwsem.h | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) (limited to 'include/linux/rwsem.h') diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 2ea18a3def04..148983e21d47 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -34,12 +34,12 @@ */ struct rw_semaphore { atomic_long_t count; -#ifdef CONFIG_RWSEM_SPIN_ON_OWNER /* - * Write owner. Used as a speculative check to see - * if the owner is running on the cpu. + * Write owner or one of the read owners. Can be used as a + * speculative check to see if the owner is running on the cpu. */ struct task_struct *owner; +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER struct optimistic_spin_queue osq; /* spinner MCS lock */ #endif raw_spinlock_t wait_lock; @@ -73,13 +73,14 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem) #endif #ifdef CONFIG_RWSEM_SPIN_ON_OWNER -#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL +#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED #else #define __RWSEM_OPT_INIT(lockname) #endif #define __RWSEM_INITIALIZER(name) \ { __RWSEM_INIT_COUNT(name), \ + .owner = NULL, \ .wait_list = LIST_HEAD_INIT((name).wait_list), \ .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \ __RWSEM_OPT_INIT(name) \ -- cgit v1.2.3 From 02f1082b003a0cd48f48f12533d969cdbf1c2b63 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Mon, 20 May 2019 16:59:10 -0400 Subject: locking/rwsem: Clarify usage of owner's nonspinaable bit Bit 1 of sem->owner (RWSEM_ANONYMOUSLY_OWNED) is used to designate an anonymous owner - readers or an anonymous writer. The setting of this anonymous bit is used as an indicator that optimistic spinning cannot be done on this rwsem. With the upcoming reader optimistic spinning patches, a reader-owned rwsem can be spinned on for a limit period of time. We still need this bit to indicate a rwsem is nonspinnable, but not setting this bit loses its meaning that the owner is known. So rename the bit to RWSEM_NONSPINNABLE to clarify its meaning. This patch also fixes a DEBUG_RWSEMS_WARN_ON() bug in __up_write(). Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen Cc: Will Deacon Cc: huang ying Link: https://lkml.kernel.org/r/20190520205918.22251-12-longman@redhat.com Signed-off-by: Ingo Molnar --- include/linux/rwsem.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/rwsem.h') diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 148983e21d47..bb76e82398b2 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -50,7 +50,7 @@ struct rw_semaphore { }; /* - * Setting bit 1 of the owner field but not bit 0 will indicate + * Setting all bits of the owner field except bit 0 will indicate * that the rwsem is writer-owned with an unknown owner. */ #define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-2L) -- cgit v1.2.3 From 94a9717b3c40e77a54e4afacd8f19a9a86bfeead Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Mon, 20 May 2019 16:59:12 -0400 Subject: locking/rwsem: Make rwsem->owner an atomic_long_t The rwsem->owner contains not just the task structure pointer, it also holds some flags for storing the current state of the rwsem. Some of the flags may have to be atomically updated. To reflect the new reality, the owner is now changed to an atomic_long_t type. New helper functions are added to properly separate out the task structure pointer and the embedded flags. Suggested-by: Peter Zijlstra Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Thomas Gleixner Cc: Tim Chen Cc: Will Deacon Cc: huang ying Link: https://lkml.kernel.org/r/20190520205918.22251-14-longman@redhat.com Signed-off-by: Ingo Molnar --- include/linux/rwsem.h | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) (limited to 'include/linux/rwsem.h') diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index bb76e82398b2..e401358c4e7e 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -35,10 +35,11 @@ struct rw_semaphore { atomic_long_t count; /* - * Write owner or one of the read owners. Can be used as a - * speculative check to see if the owner is running on the cpu. + * Write owner or one of the read owners as well flags regarding + * the current state of the rwsem. Can be used as a speculative + * check to see if the write owner is running on the cpu. */ - struct task_struct *owner; + atomic_long_t owner; #ifdef CONFIG_RWSEM_SPIN_ON_OWNER struct optimistic_spin_queue osq; /* spinner MCS lock */ #endif @@ -53,7 +54,7 @@ struct rw_semaphore { * Setting all bits of the owner field except bit 0 will indicate * that the rwsem is writer-owned with an unknown owner. */ -#define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-2L) +#define RWSEM_OWNER_UNKNOWN (-2L) /* In all implementations count != 0 means locked */ static inline int rwsem_is_locked(struct rw_semaphore *sem) @@ -80,7 +81,7 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem) #define __RWSEM_INITIALIZER(name) \ { __RWSEM_INIT_COUNT(name), \ - .owner = NULL, \ + .owner = ATOMIC_LONG_INIT(0), \ .wait_list = LIST_HEAD_INIT((name).wait_list), \ .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \ __RWSEM_OPT_INIT(name) \ -- cgit v1.2.3 From 387b14684f94483cbbb72843db406ec9a8d0d6d2 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Wed, 10 Apr 2019 08:32:41 -0300 Subject: docs: locking: convert docs to ReST and rename to *.rst Convert the locking documents to ReST and add them to the kernel development book where it belongs. Most of the stuff here is just to make Sphinx to properly parse the text file, as they're already in good shape, not requiring massive changes in order to be parsed. The conversion is actually: - add blank lines and identation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab Acked-by: Federico Vaga --- include/linux/rwsem.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/rwsem.h') diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index e401358c4e7e..9d9c663987d8 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -160,7 +160,7 @@ extern void downgrade_write(struct rw_semaphore *sem); * static then another method for expressing nested locking is * the explicit definition of lock class keys and the use of * lockdep_set_class() at lock initialization time. - * See Documentation/locking/lockdep-design.txt for more details.) + * See Documentation/locking/lockdep-design.rst for more details.) */ extern void down_read_nested(struct rw_semaphore *sem, int subclass); extern void down_write_nested(struct rw_semaphore *sem, int subclass); -- cgit v1.2.3