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block: fix request sorting at unplug 

Comparison function for list_sort() must be anticommutative,
otherwise it is not sorting in ordinary meaning.

But fortunately list_sort() always check ((*cmp)(priv, a, b) <= 0)
it not distinguish negative and zero, so comparison function can
implement only less-or-equal instead of full three-way comparison.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Konstantin Khlebnikov 2011-04-04 00:15:02 +02:00 committed by Jens Axboe
parent a63a5cf84d
commit f83e826181
1 changed files with 1 additions and 1 deletions
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2
block/blk-core.c
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@ -2665,7 +2665,7 @@ static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
struct request *rqa = container_of(a, struct request, queuelist);
struct request *rqb = container_of(b, struct request, queuelist);
return !(rqa->q == rqb->q);
return !(rqa->q <= rqb->q);
}
static void flush_plug_list(struct blk_plug *plug)