linux-kernel - Re: [BUG] 2.6.29-rc6-2450cf in scsi_lib.c (was: Large amount of scsi-sgpool)objects

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Date:	Thu, 5 Mar 2009 17:36:13 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	James.Bottomley@...senPartnership.com
Cc:	tglx@...utronix.de, jengelh@...ozas.de, bharrosh@...asas.com,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org
Subject: Re: [BUG] 2.6.29-rc6-2450cf in scsi_lib.c (was: Large amount of
	scsi-sgpool)objects

CC'ed Jens,

On Wed, 04 Mar 2009 22:56:29 +0000
James Bottomley <James.Bottomley@...senPartnership.com> wrote:

> On Wed, 2009-03-04 at 22:45 +0100, Thomas Gleixner wrote:
> > On Wed, 4 Mar 2009, Thomas Gleixner wrote:
> > 
> > Instrumented the code and the result of the failing request is
> > below. Looks like the function which sets up the request gets
> > nr_phys_segments wrong by one. 
> > 
> > If you need further trace data feel free to ask.
> 
> OK, the mapping all checks out correctly ... there must be something
> wrong with the way we count before mapping.

Yeah, looks we miscalculate nr_phys_segments in the merging path.

blk_recount_segments() needs to set bi_seg_front_size and
bi_seg_back_size for ll_merge_requests_fn()?

=
diff --git a/block/blk-merge.c b/block/blk-merge.c
index a104593..efb65b6 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -111,12 +111,19 @@ void blk_recalc_rq_segments(struct request *rq)
 
 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 {
+	unsigned int seg_size;
 	struct bio *nxt = bio->bi_next;
 
 	bio->bi_next = NULL;
-	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, NULL);
+	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, &seg_size);
 	bio->bi_next = nxt;
 	bio->bi_flags |= (1 << BIO_SEG_VALID);
+
+	if (bio->bi_phys_segments == 1 && seg_size > bio->bi_seg_front_size)
+		bio->bi_seg_front_size = seg_size;
+	if (bio->bi_phys_segments > bio->bi_seg_back_size)
+		bio->bi_seg_back_size = seg_size;
+
 }
 EXPORT_SYMBOL(blk_recount_segments);
 
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