[PATCH 3/4] btrfs: handle ENOMEM from btrfs_insert_dir_item() without aborting

[Jeff Layton]

Now that btrfs_insert_dir_item() returns -ENOMEM before modifying the
btree (thanks to delayed dir index pre-allocation), callers can handle
ENOMEM gracefully instead of aborting the transaction.

In btrfs_add_link(), add -ENOMEM to the set of recoverable errors
alongside -EEXIST and -EOVERFLOW. The fail_dir_item cleanup path
unwinds the inode_ref/root_ref and returns the error to userspace.

In btrfs_create_new_inode(), when btrfs_add_link() fails with -ENOMEM,
convert the newly-created inode into an orphan instead of aborting.
This is done by clearing nlink and adding an orphan item, which ensures
btrfs_evict_inode() will delete the INODE_ITEM and INODE_REF, and
crash-recovery will clean it up via orphan processing. If
btrfs_orphan_add() itself fails, we fall back to aborting.

This turns a filesystem-killing transaction abort into a graceful
-ENOMEM return to userspace for create(), mkdir(), mknod(), symlink(),
and link() operations under memory pressure.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 fs/btrfs/inode.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b7b4e6177135..4d9947ae08f7 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6676,7 +6676,20 @@ int btrfs_create_new_inode(struct btrfs_trans_handle *trans,
 	} else {
 		ret = btrfs_add_link(trans, BTRFS_I(dir), BTRFS_I(inode), name,
 				     false, BTRFS_I(inode)->dir_index);
-		if (unlikely(ret)) {
+		if (ret == -ENOMEM) {
+			/*
+			 * The ENOMEM came before the DIR_ITEM was inserted,
+			 * so the btree has our INODE_ITEM + INODE_REF but no
+			 * directory entry. Convert this into an orphan so
+			 * eviction (or crash-recovery) cleans up the inode.
+			 */
+			clear_nlink(inode);
+			ret = btrfs_orphan_add(trans, BTRFS_I(inode));
+			if (unlikely(ret))
+				btrfs_abort_transaction(trans, ret);
+			ret = -ENOMEM;
+			goto discard;
+		} else if (unlikely(ret)) {
 			btrfs_abort_transaction(trans, ret);
 			goto discard;
 		}
@@ -6738,7 +6751,7 @@ int btrfs_add_link(struct btrfs_trans_handle *trans,
 
 	ret = btrfs_insert_dir_item(trans, name, parent_inode, &key,
 				    btrfs_inode_type(inode), index, NULL);
-	if (ret == -EEXIST || ret == -EOVERFLOW)
+	if (ret == -EEXIST || ret == -EOVERFLOW || ret == -ENOMEM)
 		goto fail_dir_item;
 	else if (unlikely(ret)) {
 		btrfs_abort_transaction(trans, ret);

-- 
2.55.0