linux-kernel - [PATCH] block: fix request sorting at unplug

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Message-ID: <20110402153737.15555.75762.stgit@localhost6>
Date:	Sat, 2 Apr 2011 19:37:37 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Jens Axboe <axboe@...nel.dk>
CC:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] 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@...nvz.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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