| From 5370019dc2d2c2ff90e95d181468071362934f3a Mon Sep 17 00:00:00 2001 |
| From: Guo Chao <yan@linux.vnet.ibm.com> |
| Date: Thu, 21 Feb 2013 15:16:45 -0800 |
| Subject: loopdev: fix a deadlock |
| |
| From: Guo Chao <yan@linux.vnet.ibm.com> |
| |
| commit 5370019dc2d2c2ff90e95d181468071362934f3a upstream. |
| |
| bd_mutex and lo_ctl_mutex can be held in different order. |
| |
| Path #1: |
| |
| blkdev_open |
| blkdev_get |
| __blkdev_get (hold bd_mutex) |
| lo_open (hold lo_ctl_mutex) |
| |
| Path #2: |
| |
| blkdev_ioctl |
| 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: |
| |
| http://marc.info/?l=linux-kernel&m=123806169129727&w=2 |
| |
| 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@linux.vnet.ibm.com> |
| Cc: Alexander Viro <viro@zeniv.linux.org.uk> |
| Cc: Guo Chao <yan@linux.vnet.ibm.com> |
| Cc: M. Hindess <hindessm@uk.ibm.com> |
| Cc: Nikanth Karthikesan <knikanth@suse.de> |
| Cc: Jens Axboe <axboe@kernel.dk> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Jens Axboe <axboe@kernel.dk> |
| Acked-by: Jeff Mahoney <jeffm@suse.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/block/loop.c | 2 -- |
| 1 file changed, 2 deletions(-) |
| |
| --- a/drivers/block/loop.c |
| +++ b/drivers/block/loop.c |
| @@ -1274,11 +1274,9 @@ static int loop_set_capacity(struct loop |
| /* 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); |
| |
| out: |
| return err; |