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Subject[PATCH] block: fix request sorting at unplug
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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>
---
block/blk-core.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index e0a0623..5e151d2 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -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)


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