From 4f331f01b9c43bf001d3ffee578a97a1e0633eac Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 20 Jul 2010 15:18:07 -0700 Subject: [PATCH] vfs: don't hold s_umount over close_bdev_exclusive() call 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 Reported-by: Ciprian Docan Cc: Al Viro Acked-by: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Al Viro --- fs/super.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/super.c b/fs/super.c index 938119ab8dcb..3479ca6f005f 100644 --- a/fs/super.c +++ b/fs/super.c @@ -773,7 +773,16 @@ int get_sb_bdev(struct file_system_type *fs_type, goto error_bdev; } + /* + * s_umount nests inside bd_mutex during + * __invalidate_device(). close_bdev_exclusive() + * acquires bd_mutex and can't be called under + * s_umount. Drop s_umount temporarily. This is safe + * as we're holding an active reference. + */ + up_write(&s->s_umount); close_bdev_exclusive(bdev, mode); + down_write(&s->s_umount); } else { char b[BDEVNAME_SIZE];