From: Filipe Manana fdmanana@suse.com
commit 33fab972497ae66822c0b6846d4f9382938575b6 upstream.
When creating a subvolume, at create_subvol(), we allocate an anonymous device and later call btrfs_get_new_fs_root(), which in turn just calls btrfs_get_root_ref(). There we call btrfs_init_fs_root() which assigns the anonymous device to the root, but if after that call there's an error, when we jump to 'fail' label, we call btrfs_put_root(), which frees the anonymous device and then returns an error that is propagated back to create_subvol(). Than create_subvol() frees the anonymous device again.
When this happens, if the anonymous device was not reallocated after the first time it was freed with btrfs_put_root(), we get a kernel message like the following:
(...) [13950.282466] BTRFS: error (device dm-0) in create_subvol:663: errno=-5 IO failure [13950.283027] ida_free called for id=65 which is not allocated. [13950.285974] BTRFS info (device dm-0): forced readonly (...)
If the anonymous device gets reallocated by another btrfs filesystem or any other kernel subsystem, then bad things can happen.
So fix this by setting the root's anonymous device to 0 at btrfs_get_root_ref(), before we call btrfs_put_root(), if an error happened.
Fixes: 2dfb1e43f57dd3 ("btrfs: preallocate anon block device at first phase of snapshot creation") CC: stable@vger.kernel.org # 5.10+ Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Filipe Manana fdmanana@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/disk-io.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -1731,6 +1731,14 @@ again: } return root; fail: + /* + * If our caller provided us an anonymous device, then it's his + * responsability to free it in case we fail. So we have to set our + * root's anon_dev to 0 to avoid a double free, once by btrfs_put_root() + * and once again by our caller. + */ + if (anon_dev) + root->anon_dev = 0; btrfs_put_root(root); return ERR_PTR(ret); }