Manfred Spraul 2e094abfd1 ipc/sem.c: change memory barrier in sem_lock() to smp_rmb() ... When I fixed bugs in the sem_lock() logic, I was more conservative than necessary. Therefore it is safe to replace the smp_mb() with smp_rmb(). And: With smp_rmb(), semop() syscalls are up to 10% faster. The race we must protect against is: sem->lock is free sma->complex_count = 0 sma->sem_perm.lock held by thread B thread A: A: spin_lock(&sem->lock) B: sma->complex_count++; (now 1) B: spin_unlock(&sma->sem_perm.lock); A: spin_is_locked(&sma->sem_perm.lock); A: XXXXX memory barrier A: if (sma->complex_count == 0) Thread A must read the increased complex_count value, i.e. the read must not be reordered with the read of sem_perm.lock done by spin_is_locked(). Since it's about ordering of reads, smp_rmb() is sufficient. [akpm@linux-foundation.org: update sem_lock() comment, from Davidlohr] Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Reviewed-by: Davidlohr Bueso <dave@stgolabs.net> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2014-12-13 12:42:52 -08:00
..
compat_mq.c	ipc, kernel: use Linux headers	2014-06-06 16:08:14 -07:00
compat.c	ipc: resolve shadow warnings	2014-10-14 02:18:23 +02:00
ipc_sysctl.c	ipc: always handle a new value of auto_msgmni	2014-10-14 02:18:22 +02:00
ipcns_notifier.c
Makefile
mq_sysctl.c	ipc: convert use of typedef ctl_table to struct ctl_table	2014-06-06 16:08:16 -07:00
mqueue.c	new helper: audit_file()	2014-11-19 13:01:26 -05:00
msg.c	ipc,msg: document volatile r_msg	2014-06-06 16:08:15 -07:00
msgutil.c
namespace.c	namespaces: Use task_lock and not rcu to protect nsproxy	2014-07-29 18:08:50 -07:00
sem.c	ipc/sem.c: change memory barrier in sem_lock() to smp_rmb()	2014-12-13 12:42:52 -08:00
shm.c	ipc/shm: kill the historical/wrong mm->start_stack check	2014-10-14 02:18:23 +02:00
syscall.c
util.c	ipc/util.c: use __seq_open_private() instead of seq_open()	2014-10-14 02:18:23 +02:00
util.h	ipc, kernel: clear whitespace	2014-06-06 16:08:14 -07:00