Linus Torvalds 04e2f1741d Add memory barrier semantics to wake_up() & co ... Oleg Nesterov and others have pointed out that on some architectures, the traditional sequence of set_current_state(TASK_INTERRUPTIBLE); if (CONDITION) return; schedule(); is racy wrt another CPU doing CONDITION = 1; wake_up_process(p); because while set_current_state() has a memory barrier separating setting of the TASK_INTERRUPTIBLE state from reading of the CONDITION variable, there is no such memory barrier on the wakeup side. Now, wake_up_process() does actually take a spinlock before it reads and sets the task state on the waking side, and on x86 (and many other architectures) that spinlock is in fact equivalent to a memory barrier, but that is not generally guaranteed. The write that sets CONDITION could move into the critical region protected by the runqueue spinlock. However, adding a smp_wmb() to before the spinlock should now order the writing of CONDITION wrt the lock itself, which in turn is ordered wrt the accesses within the spinlock (which includes the reading of the old state). This should thus close the race (which probably has never been seen in practice, but since smp_wmb() is a no-op on x86, it's not like this will make anything worse either on the most common architecture where the spinlock already gave the required protection). Acked-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Dmitry Adamushko <dmitry.adamushko@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2008-02-23 18:05:03 -08:00
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.gitignore
acct.c
audit_tree.c
audit.c
audit.h
auditfilter.c
auditsc.c
backtracetest.c
capability.c
cgroup_debug.c
cgroup.c	cgroup: remove dead code in cgroup_get_rootdir()	2008-02-23 17:13:25 -08:00
compat.c
configs.c
cpu.c
cpuset.c
delayacct.c
dma.c
exec_domain.c
exit.c
extable.c
fork.c
futex_compat.c	futex: runtime enable pi and robust functionality	2008-02-23 17:12:15 -08:00
futex.c	futex: runtime enable pi and robust functionality	2008-02-23 17:12:15 -08:00
hrtimer.c
itimer.c
kallsyms.c
Kconfig.hz
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kfifo.c
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lockdep.c
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mutex-debug.c
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rtmutex_common.h
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rtmutex.c
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sched_debug.c
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sched_idletask.c
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sched_stats.h
sched.c	Add memory barrier semantics to wake_up() & co	2008-02-23 18:05:03 -08:00
seccomp.c
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softirq.c
softlockup.c
spinlock.c
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