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

--
Jens Axboe

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