Re: [PATCH] splice : two smp_mb() can be omitted

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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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