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authorOleg Nesterov <oleg@redhat.com>2013-08-12 18:14:00 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-01-09 12:24:23 -0800
commit57f74b6ecebf59991677dd2da0f0433e8be6c945 (patch)
tree4e3b332c34f41796e61bf7bcfb3e6bb06386e0b3 /arch/x86
parenta29ccdd1b5a61fad7d4883b3ef63da3a313f1e44 (diff)
downloadlinaro-lsk-57f74b6ecebf59991677dd2da0f0433e8be6c945.tar.gz
sched: fix the theoretical signal_wake_up() vs schedule() race
commit e0acd0a68ec7dbf6b7a81a87a867ebd7ac9b76c4 upstream. This is only theoretical, but after try_to_wake_up(p) was changed to check p->state under p->pi_lock the code like __set_current_state(TASK_INTERRUPTIBLE); schedule(); can miss a signal. This is the special case of wait-for-condition, it relies on try_to_wake_up/schedule interaction and thus it does not need mb() between __set_current_state() and if(signal_pending). However, this __set_current_state() can move into the critical section protected by rq->lock, now that try_to_wake_up() takes another lock we need to ensure that it can't be reordered with "if (signal_pending(current))" check inside that section. The patch is actually one-liner, it simply adds smp_wmb() before spin_lock_irq(rq->lock). This is what try_to_wake_up() already does by the same reason. We turn this wmb() into the new helper, smp_mb__before_spinlock(), for better documentation and to allow the architectures to change the default implementation. While at it, kill smp_mb__after_lock(), it has no callers. Perhaps we can also add smp_mb__before/after_spinunlock() for prepare_to_wait(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/include/asm/spinlock.h4
1 files changed, 0 insertions, 4 deletions
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 33692eaabab..e3ddd7db723 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -233,8 +233,4 @@ static inline void arch_write_unlock(arch_rwlock_t *rw)
#define arch_read_relax(lock) cpu_relax()
#define arch_write_relax(lock) cpu_relax()
-/* The {read|write|spin}_lock() on x86 are full memory barriers. */
-static inline void smp_mb__after_lock(void) { }
-#define ARCH_HAS_SMP_MB_AFTER_LOCK
-
#endif /* _ASM_X86_SPINLOCK_H */