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发表于 2011-10-14 13:26
这是我在kernel log 发现的。。。- Author: Nicolas Pitre <nico@cam.org>
- Date: Wed Dec 21 12:26:25 2005 -0500
- [PATCH] fix race with preempt_enable()
-
- Currently a simple
-
- void foo(void) { preempt_enable(); }
-
- produces the following code on ARM:
-
- foo:
- bic r3, sp, #8128
- bic r3, r3, #63
- ldr r2, [r3, #4]
- ldr r1, [r3, #0]
- sub r2, r2, #1
- tst r1, #4
- str r2, [r3, #4]
- blne preempt_schedule
- mov pc, lr
-
- The problem is that the TIF_NEED_RESCHED flag is loaded _before_ the
- preemption count is stored back, hence any interrupt coming within that
- 3 instruction window causing TIF_NEED_RESCHED to be set won't be
- seen and scheduling won't happen as it should.
-
- Nothing currently prevents gcc from performing that reordering. There
- is already a barrier() before the decrement of the preemption count, but
- another one is needed between this and the TIF_NEED_RESCHED flag test
- for proper code ordering.
-
- Signed-off-by: Nicolas Pitre <nico@cam.org>
- Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
- Signed-off-by: Linus Torvalds <torvalds@osdl.org>
- diff --git a/include/linux/preempt.h b/include/linux/preempt.h
- index d9a2f52..5769d14 100644
- --- a/include/linux/preempt.h
- +++ b/include/linux/preempt.h
- @@ -48,6 +48,7 @@ do { \
- #define preempt_enable() \
- do { \
- preempt_enable_no_resched(); \
- + barrier(); \
- preempt_check_resched(); \
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