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blk: clean up plug

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Current code looks like inner plug gets flushed with a
blk_finish_plug(). Actually it's a nop. All requests/callbacks are added
to current->plug, while only outmost plug is assigned to current->plug.
So inner plug always has empty request/callback list, which makes
blk_flush_plug_list() a nop. This tries to make the code more clear.

Signed-off-by: Shaohua Li <shli@fb.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Shaohua Li 2015-05-08 10:51:28 -07:00 committed by Jens Axboe
parent 9dc6c806b3
commit dd6cf3e18d
1 changed files with 12 additions and 12 deletions
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24
block/blk-core.c
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@ -3032,21 +3032,20 @@ void blk_start_plug(struct blk_plug *plug)
{ {
struct task_struct *tsk = current; struct task_struct *tsk = current;
/*
* If this is a nested plug, don't actually assign it.
*/
if (tsk->plug)
return;
INIT_LIST_HEAD(&plug->list); INIT_LIST_HEAD(&plug->list);
INIT_LIST_HEAD(&plug->mq_list); INIT_LIST_HEAD(&plug->mq_list);
INIT_LIST_HEAD(&plug->cb_list); INIT_LIST_HEAD(&plug->cb_list);
/* /*
* If this is a nested plug, don't actually assign it. It will be * Store ordering should not be needed here, since a potential
* flushed on its own. * preempt will imply a full memory barrier
*/ */
if (!tsk->plug) { tsk->plug = plug;
/*
* Store ordering should not be needed here, since a potential
* preempt will imply a full memory barrier
*/
tsk->plug = plug;
}
} }
EXPORT_SYMBOL(blk_start_plug); EXPORT_SYMBOL(blk_start_plug);
@ -3193,10 +3192,11 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
void blk_finish_plug(struct blk_plug *plug) void blk_finish_plug(struct blk_plug *plug)
{ {
if (plug != current->plug)
return;
blk_flush_plug_list(plug, false); blk_flush_plug_list(plug, false);
if (plug == current->plug) current->plug = NULL;
current->plug = NULL;
} }
EXPORT_SYMBOL(blk_finish_plug); EXPORT_SYMBOL(blk_finish_plug);