-
Tejun Heo authored
Fix an obscure AB-BA deadlock in get_sb_bdev(). When a superblock is mounted more than once get_sb_bdev() calls close_bdev_exclusive() to drop the extra bdev reference while holding s_umount. However, sb->s_umount nests inside bd_mutex during __invalidate_device() and close_bdev_exclusive() acquires bd_mutex during blkdev_put(); thus creating an AB-BA deadlock. This condition doesn't trigger frequently. For this condition to be visible to lockdep, the filesystem must occupy the whole device (as __invalidate_device() only grabs bd_mutex for the whole device), the FS must be mounted more than once and partition rescan should be issued while the FS is still mounted. Fix it by dropping s_umount over close_bdev_exclusive(). Signed-off-by:
Tejun Heo <tj@kernel.org> Reported-by:
Ciprian Docan <docan@eden.rutgers.edu> Cc: Al Viro <viro@zeniv.linux.org.uk> Acked-by:
Jens Axboe <axboe@kernel.dk> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Al Viro <viro@zeniv.linux.org.uk>
4f331f01