Btrfs: don't invalidate root dentry when subvolume deletion fails

commit 64ad6c488975d7516230cf7849190a991fd615ae upstream.

Since commit bafc9b754f75 ("vfs: More precise tests in d_invalidate"),
mounted subvolumes can be deleted because d_invalidate() won't fail.
However, we run into problems when we attempt to delete the default
subvolume while it is mounted as the root filesystem:

	# btrfs subvol list /
	ID 257 gen 306 top level 5 path rootvol
	ID 267 gen 334 top level 5 path snap1
	# btrfs subvol get-default /
	ID 267 gen 334 top level 5 path snap1
	# btrfs inspect-internal rootid /
	267
	# mount -o subvol=/ /dev/vda1 /mnt
	# btrfs subvol del /mnt/snap1
	Delete subvolume (no-commit): '/mnt/snap1'
	ERROR: cannot delete '/mnt/snap1' - Operation not permitted
	# findmnt /
	findmnt: can't read /proc/mounts: No such file or directory
	# ls /proc
	#

Markus reported that this same scenario simply led to a kernel oops.

This happens because in btrfs_ioctl_snap_destroy(), we call
d_invalidate() before we check may_destroy_subvol(), which means that we
detach the submounts and drop the dentry before erroring out. Instead,
we should only invalidate the dentry once the deletion has succeeded.
Additionally, the shrink_dcache_sb() isn't necessary; d_invalidate()
will prune the dcache for the deleted subvolume.

Fixes: bafc9b754f75 ("vfs: More precise tests in d_invalidate")
Reported-by: Markus Schauler <mschauler@gmail.com>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 54b1fb57886f3b2a7be247937efa26d6e305aaa4)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 7ad20f4acae9657372935e7ffc1ca398ba074b10..24809b2c45259d778aa4c896e08d8fd28bcfd06f 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2407,8 +2407,6 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
                goto out_unlock_inode;
        }
 
-       d_invalidate(dentry);
-
        down_write(&root->fs_info->subvol_sem);
 
        err = may_destroy_subvol(dest);
@@ -2502,7 +2500,7 @@ out_up_write:
 out_unlock_inode:
        mutex_unlock(&inode->i_mutex);
        if (!err) {
-               shrink_dcache_sb(root->fs_info->sb);
+               d_invalidate(dentry);
                btrfs_invalidate_inodes(dest);
                d_delete(dentry);
                ASSERT(dest->send_in_progress == 0);