Patchwork [025/150] loopdev: fix a deadlock

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Submitter Luis Henriques
Date March 26, 2013, 3:18 p.m.
Message ID <>
Download mbox | patch
Permalink /patch/231412/
State New
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Luis Henriques - March 26, 2013, 3:18 p.m. -stable review patch.  If anyone has any objections, please let me know.


From: Guo Chao <>

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 <>
Cc: Alexander Viro <>
Cc: Guo Chao <>
Cc: M. Hindess <>
Cc: Nikanth Karthikesan <>
Cc: Jens Axboe <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Jens Axboe <>
Signed-off-by: Luis Henriques <>
 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;