linux-kernel - [PATCH] xen-blkback: fix dispatch_rw_block

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Date:	Mon, 11 Mar 2013 09:39:55 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:	"Jens Axboe" <axboe@...nel.dk>,
	"xen-devel" <xen-devel@...ts.xen.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH] xen-blkback: fix dispatch_rw_block_io() error path

Commit 7708992 ("xen/blkback: Seperate the bio allocation and the bio
submission") consolidated the pendcnt updates to just a single write,
neglecting the fact that the error path relied on it getting set to 1
up front (such that the decrement in __end_block_io_op() would actually
drop the count to zero, triggering the necessary cleanup actions).

Also remove a misleading and a stale (after said commit) comment.

Signed-off-by: Jan Beulich <jbeulich@...e.com>

---
 drivers/block/xen-blkback/blkback.c |    7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

--- 3.9-rc2/drivers/block/xen-blkback/blkback.c
+++ 3.9-rc2-xen-blkback-error-path-refcnt/drivers/block/xen-blkback/blkback.c
@@ -977,13 +977,7 @@ static int dispatch_rw_block_io(struct x
 		bio->bi_end_io  = end_block_io_op;
 	}
 
-	/*
-	 * We set it one so that the last submit_bio does not have to call
-	 * atomic_inc.
-	 */
 	atomic_set(&pending_req->pendcnt, nbio);
-
-	/* Get a reference count for the disk queue and start sending I/O */
 	blk_start_plug(&plug);
 
 	for (i = 0; i < nbio; i++)
@@ -1011,6 +1005,7 @@ static int dispatch_rw_block_io(struct x
  fail_put_bio:
 	for (i = 0; i < nbio; i++)
 		bio_put(biolist[i]);
+	atomic_set(&pending_req->pendcnt, 1);
 	__end_block_io_op(pending_req, -EINVAL);
 	msleep(1); /* back off a bit */
 	return -EIO;




View attachment "linux-3.9-rc2-xen-blkback-error-path-refcnt.patch" of type "text/plain" (1388 bytes)