Messages in this thread | | | From | Eric Dumazet <> | Subject | Re: [PATCH] splice : two smp_mb() can be omitted | Date | Tue, 31 Oct 2006 11:51:32 +0100 |
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On Tuesday 31 October 2006 10:40, Nick Piggin wrote:
> Uh, there is nothing that says mutex_unlock or any unlock > functions contain an implicit smp_mb(). What is given is that the > lock and unlock obey aquire and release memory ordering, > respectively. > > a = x; > xxx_unlock > b = y; > > In this situation, the load of y can be executed before that of x. > And some architectures will even do so (i386 can, because the > unlock is an unprefixed store; ia64 can, because it uses a release > barrier in the unlock).
Hum... it seems your mutex_unlock() i386/x86_64 copy is not same as mine :)
Maybe we could document the fact that mutex_{lock|unlock}() has or has not an implicit smp_mb().
If not, delete smp_mb() calls from include/asm-generic/mutex-dec.h
Ingo ?
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