6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Omar Sandoval <osandov@xxxxxx>
commit 3324d0547861b16cf436d54abba7052e0c8aa9de upstream.
Sweet Tea spotted a race between subvolume deletion and snapshotting
that can result in the root item for the snapshot having the
BTRFS_ROOT_SUBVOL_DEAD flag set. The race is:
Thread 1 | Thread 2
----------------------------------------------|----------
btrfs_delete_subvolume |
btrfs_set_root_flags(BTRFS_ROOT_SUBVOL_DEAD)|
|btrfs_mksubvol
| down_read(subvol_sem)
| create_snapshot
| ...
| create_pending_snapshot
| copy root item from source
down_write(subvol_sem) |
This flag is only checked in send and swap activate, which this would
cause to fail mysteriously.
create_snapshot() now checks the root refs to reject a deleted
subvolume, so we can fix this by locking subvol_sem earlier so that the
BTRFS_ROOT_SUBVOL_DEAD flag and the root refs are updated atomically.
CC: stable@xxxxxxxxxxxxxxx # 4.14+
Reported-by: Sweet Tea Dorminy <sweettea-kernel@xxxxxxxxxx>
Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@xxxxxxxxxx>
Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx>
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/inode.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4689,6 +4689,8 @@ int btrfs_delete_subvolume(struct inode
u64 root_flags;
int ret;
+ down_write(&fs_info->subvol_sem);
+
/*
* Don't allow to delete a subvolume with send in progress. This is
* inside the inode lock so the error handling that has to drop the bit
@@ -4700,25 +4702,25 @@ int btrfs_delete_subvolume(struct inode
btrfs_warn(fs_info,
"attempt to delete subvolume %llu during send",
dest->root_key.objectid);
- return -EPERM;
+ ret = -EPERM;
+ goto out_up_write;
}
if (atomic_read(&dest->nr_swapfiles)) {
spin_unlock(&dest->root_item_lock);
btrfs_warn(fs_info,
"attempt to delete subvolume %llu with active swapfile",
root->root_key.objectid);
- return -EPERM;
+ ret = -EPERM;
+ goto out_up_write;
}
root_flags = btrfs_root_flags(&dest->root_item);
btrfs_set_root_flags(&dest->root_item,
root_flags | BTRFS_ROOT_SUBVOL_DEAD);
spin_unlock(&dest->root_item_lock);
- down_write(&fs_info->subvol_sem);
-
ret = may_destroy_subvol(dest);
if (ret)
- goto out_up_write;
+ goto out_undead;
btrfs_init_block_rsv(&block_rsv, BTRFS_BLOCK_RSV_TEMP);
/*
@@ -4728,7 +4730,7 @@ int btrfs_delete_subvolume(struct inode
*/
ret = btrfs_subvolume_reserve_metadata(root, &block_rsv, 5, true);
if (ret)
- goto out_up_write;
+ goto out_undead;
trans = btrfs_start_transaction(root, 0);
if (IS_ERR(trans)) {
@@ -4794,15 +4796,17 @@ out_end_trans:
inode->i_flags |= S_DEAD;
out_release:
btrfs_subvolume_release_metadata(root, &block_rsv);
-out_up_write:
- up_write(&fs_info->subvol_sem);
+out_undead:
if (ret) {
spin_lock(&dest->root_item_lock);
root_flags = btrfs_root_flags(&dest->root_item);
btrfs_set_root_flags(&dest->root_item,
root_flags & ~BTRFS_ROOT_SUBVOL_DEAD);
spin_unlock(&dest->root_item_lock);
- } else {
+ }
+out_up_write:
+ up_write(&fs_info->subvol_sem);
+ if (!ret) {
d_invalidate(dentry);
btrfs_prune_dentries(dest);
ASSERT(dest->send_in_progress == 0);
