[ 3.5.y.z extended stable ] Patch "loopdev: fix a deadlock" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Tue Mar 19 15:04:29 UTC 2013

This is a note to let you know that I have just added a patch titled

    loopdev: fix a deadlock

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From 9197d80d8c71433aca94b206582b9446dce6637c Mon Sep 17 00:00:00 2001
From: Guo Chao <yan at linux.vnet.ibm.com>
Date: Thu, 21 Feb 2013 15:16:45 -0800
Subject: [PATCH] loopdev: fix a deadlock

commit 5370019dc2d2c2ff90e95d181468071362934f3a upstream.

bd_mutex and lo_ctl_mutex can be held in different order.

Path #1:

  __blkdev_get (hold bd_mutex)
   lo_open (hold lo_ctl_mutex)

Path #2:

 lo_ioctl (hold lo_ctl_mutex)
  lo_set_capacity (hold bd_mutex)

Lockdep does not report it, because path #2 actually holds a subclass of
lo_ctl_mutex.  This subclass seems creep into the code by mistake.  The
patch author actually just mentioned it in the changelog, see commit
f028f3b2 ("loop: fix circular locking in loop_clr_fd()"), also see:


Path #2 hold bd_mutex to call bd_set_size(), I've protected it
with i_mutex in a previous patch, so drop bd_mutex at this site.

Signed-off-by: Guo Chao <yan at linux.vnet.ibm.com>
Cc: Alexander Viro <viro at zeniv.linux.org.uk>
Cc: Guo Chao <yan at linux.vnet.ibm.com>
Cc: M. Hindess <hindessm at uk.ibm.com>
Cc: Nikanth Karthikesan <knikanth at suse.de>
Cc: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 drivers/block/loop.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 3bba655..11e702c 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1263,11 +1263,9 @@ static int loop_set_capacity(struct loop_device *lo, struct block_device *bdev)
 	/* the width of sector_t may be narrow for bit-shift */
 	sz = sec;
 	sz <<= 9;
-	mutex_lock(&bdev->bd_mutex);
 	bd_set_size(bdev, sz);
 	/* let user-space know about the new size */
 	kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
-	mutex_unlock(&bdev->bd_mutex);

 	return err;

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