[PATCH] btrfs: don't force the filesystem read-only on EDQUOT/ENOSPC verity rollback

[Daniel Linjama <daniel@dev.linjama.com>]

When enable_verity() hits the qgroup limit, rollback_verity() needs its
own metadata reservation. When the qgroup limit refuses the rollback,
the whole filesystem is forced read-only even though the qgroup limit
was for one subvolume only.

Skip btrfs_handle_fs_error() for -EDQUOT/-ENOSPC and just return the
error. The verity orphan item is left in place but the orphan cleanup
from commit 705242538ff3 ("btrfs: verity metadata orphan items") will
remove it at the next mount. fsverity enable still correctly fails but
the filesystem is not forced read-only.

Fixes: 146054090b08 ("btrfs: initial fsverity support")
Signed-off-by: Daniel Linjama <daniel@dev.linjama.com>
---
Verified on a virtual machine with a mainline kernel (08df884136f1) and
a loop-mounted btrfs, with either a qgroup limit on a subvolume or a
full filesystem. On the unpatched kernel the whole filesystem was forced
read-only. On the patched kernel fsverity enable returns -EDQUOT/-ENOSPC
and the filesystem stays read-write.

 fs/btrfs/verity.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/verity.c b/fs/btrfs/verity.c
index 4e0ab5842274..8d0f9eea4c39 100644
--- a/fs/btrfs/verity.c
+++ b/fs/btrfs/verity.c
@@ -441,7 +441,9 @@ static int del_orphan(struct btrfs_trans_handle *trans, struct btrfs_inode *inod
  *
  * We try to handle recoverable errors while enabling verity by rolling it back
  * and just failing the operation, rather than having an fs level error no
- * matter what. However, any error in rollback is unrecoverable.
+ * matter what. Failing to delete the verity items for lack of space is
+ * tolerated, the orphan item ensures they are removed on the next mount.
+ * Any other error in rollback is unrecoverable.
  *
  * Returns 0 on success, negative error code on failure.
  */
@@ -456,9 +458,21 @@ static int rollback_verity(struct btrfs_inode *inode)
 	clear_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &inode->runtime_flags);
 	ret = btrfs_drop_verity_items(inode);
 	if (ret) {
-		btrfs_handle_fs_error(root->fs_info, ret,
-				"failed to drop verity items in rollback %llu",
-				inode->vfs_inode.i_ino);
+		/*
+		 * -EDQUOT and -ENOSPC mean we could not reserve metadata to
+		 * delete the verity items. That is not a consistency problem,
+		 * so don't turn the filesystem read-only. Leave the items and
+		 * the orphan in place, orphan cleanup on the next mount will
+		 * remove them.
+		 */
+		if (ret != -EDQUOT && ret != -ENOSPC)
+			btrfs_handle_fs_error(root->fs_info, ret,
+					      "failed to drop verity items in rollback %llu",
+					      inode->vfs_inode.i_ino);
+		else
+			btrfs_warn(root->fs_info,
+				   "failed to drop verity items in rollback %llu: %pe",
+				   inode->vfs_inode.i_ino, ERR_PTR(ret));
 		goto out;
 	}
 
-- 
2.55.0