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SubjectRe: [PATCH] splice : two smp_mb() can be omitted
Jens Axboe a écrit :
> On Tue, Oct 31 2006, Eric Dumazet wrote:
>> This patch deletes two calls to smp_mb() that were done after
>> mutex_unlock() that contains an implicit memory barrier.
>>
>> The first one in splice_to_pipe(), where 'do_wakeup' is set to true only if
>> pipe->inode is set (and in this case the
>> if (pipe->inode)
>> mutex_unlock(&pipe->inode->i_mutex);
>> is done too)
>>
>> The second one in link_pipe(), following inode_double_unlock() that
>> contains calls to mutex_unlock() too.
>
> NAK on that patch, the smp_mb() follows the waitqueue_active(). If you
> later change the code and move the locks or whatnot, you have lost that
> connection.
>
> If you change the patch to insert a comment, then it may be more
> applicable.
>

Hum... I read fs/pipe.c and see no smp_mb() there, but I suspect same
semantics are/were used.

Should we add comments on fs/pipe.c too ?

Eric
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