On Fri, 2013-03-15 at 18:24 -0400, Jeff Mahoney wrote:
> 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@xxxxxxxxxxxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Guo Chao <yan@xxxxxxxxxxxxxxxxxx>
> Cc: M. Hindess <hindessm@xxxxxxxxxx>
> Cc: Nikanth Karthikesan <knikanth@xxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # 3.0 3.2 3.4 3.8 d646a02a block: use i_size_write() in bd_set_size()
> Cc: stable@xxxxxxxxxxxxxxx # 3.0 3.2 3.4 3.8
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> Acked-by: Jeff Mahoney <jeffm@xxxxxxxx>
[...]
Queued up for 3.2, thanks.
Ben.
--
Ben Hutchings
Never attribute to conspiracy what can adequately be explained by stupidity.
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