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authorOmar Sandoval <osandov@fb.com>2024-01-04 22:48:47 +0300
committerDavid Sterba <dsterba@suse.com>2024-01-12 04:00:21 +0300
commit3324d0547861b16cf436d54abba7052e0c8aa9de (patch)
treed824794b53f6050ba78af828f876cbce3cc0a91b /fs/btrfs
parent7081929ab2572920e94d70be3d332e5c9f97095a (diff)
downloadlinux-3324d0547861b16cf436d54abba7052e0c8aa9de.tar.xz
btrfs: avoid copying BTRFS_ROOT_SUBVOL_DEAD flag to snapshot of subvolume being deleted
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@vger.kernel.org # 4.14+ Reported-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me> Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me> Reviewed-by: Anand Jain <anand.jain@oracle.com> Signed-off-by: Omar Sandoval <osandov@fb.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs')
-rw-r--r--fs/btrfs/inode.c22
1 files changed, 13 insertions, 9 deletions
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b3e39610cc95..7bcc1c03437a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4458,6 +4458,8 @@ int btrfs_delete_subvolume(struct btrfs_inode *dir, struct dentry *dentry)
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
@@ -4469,25 +4471,25 @@ int btrfs_delete_subvolume(struct btrfs_inode *dir, struct dentry *dentry)
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);
/*
@@ -4497,7 +4499,7 @@ int btrfs_delete_subvolume(struct btrfs_inode *dir, struct dentry *dentry)
*/
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)) {
@@ -4563,15 +4565,17 @@ 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);