btrfs: fix log tree replay failure due to file with 0 links and extents

If we log a new inode (not persisted in a past transaction) that has 0
links and extents, then log another inode with an higher inode number, we
end up with failing to replay the log tree with -EINVAL. The steps for
this are:

1) create new file A
2) write some data to file A
3) open an fd on file A
4) unlink file A
5) fsync file A using the previously open fd
6) create file B (has higher inode number than file A)
7) fsync file B
8) power fail before current transaction commits

Now when attempting to mount the fs, the log replay will fail with
-ENOENT at replay_one_extent() when attempting to replay the first
extent of file A. The failure comes when trying to open the inode for
file A in the subvolume tree, since it doesn't exist.

Before commit 5f61b96 ("btrfs: fix inode lookup error handling
during log replay"), the returned error was -EIO instead of -ENOENT,
since we converted any errors when attempting to read an inode during
log replay to -EIO.

The reason for this is that the log replay procedure fails to ignore
the current inode when we are at the stage LOG_WALK_REPLAY_ALL, our
current inode has 0 links and last inode we processed in the previous
stage has a non 0 link count. In other words, the issue is that at
replay_one_extent() we only update wc->ignore_cur_inode if the current
replay stage is LOG_WALK_REPLAY_INODES.

Fix this by updating wc->ignore_cur_inode whenever we find an inode item
regardless of the current replay stage. This is a simple solution and easy
to backport, but later we can do other alternatives like avoid logging
extents or inode items other than the inode item for inodes with a link
count of 0.

The problem with the wc->ignore_cur_inode logic has been around since
commit f2d72f4 ("Btrfs: fix warning when replaying log after fsync
of a tmpfile") but it only became frequent to hit since the more recent
commit 5e85262 ("btrfs: fix fsync of files with no hard links not
persisting deletion"), because we stopped skipping inodes with a link
count of 0 when logging, while before the problem would only be triggered
if trying to replay a log tree created with an older kernel which has a
logged inode with 0 links.

A test case for fstests will be submitted soon.

Reported-by: Peter Jung <[email protected]>
Link: https://lore.kernel.org/linux-btrfs/[email protected]/
Reported-by: burneddi <[email protected]>
Link: https://lore.kernel.org/linux-btrfs/lh4W-Lwc0Mbk-QvBhhQyZxf6VbM3E8VtIvU3fPIQgweP_Q1n7wtlUZQc33sYlCKYd-o6rryJQfhHaNAOWWRKxpAXhM8NZPojzsJPyHMf2qY=@protonmail.com/#t
Reported-by: Russell Haley <[email protected]>
Link: https://lore.kernel.org/linux-btrfs/[email protected]/
Fixes: f2d72f4 ("Btrfs: fix warning when replaying log after fsync of a tmpfile")
Reviewed-by: Boris Burkov <[email protected]>
Signed-off-by: Filipe Manana <[email protected]>

Author: fdmanana

fs/btrfs/tree-log.c

@@ -321,8 +321,7 @@ struct walk_control {
 
 	/*
 	 * Ignore any items from the inode currently being processed. Needs
-	 * to be set every time we find a BTRFS_INODE_ITEM_KEY and we are in
-	 * the LOG_WALK_REPLAY_INODES stage.
+	 * to be set every time we find a BTRFS_INODE_ITEM_KEY.
 	 */
 	bool ignore_cur_inode;
 
@@ -2602,30 +2601,44 @@ static int replay_one_buffer(struct btrfs_root *log, struct extent_buffer *eb,
 
 	nritems = btrfs_header_nritems(eb);
 	for (i = 0; i < nritems; i++) {
-		btrfs_item_key_to_cpu(eb, &key, i);
+		struct btrfs_inode_item *inode_item;
 
-		/* inode keys are done during the first stage */
-		if (key.type == BTRFS_INODE_ITEM_KEY &&
-		    wc->stage == LOG_WALK_REPLAY_INODES) {
-			struct btrfs_inode_item *inode_item;
-			u32 mode;
+		btrfs_item_key_to_cpu(eb, &key, i);
 
-			inode_item = btrfs_item_ptr(eb, i,
-					    struct btrfs_inode_item);
+		if (key.type == BTRFS_INODE_ITEM_KEY) {
+			inode_item = btrfs_item_ptr(eb, i, struct btrfs_inode_item);
 			/*
-			 * If we have a tmpfile (O_TMPFILE) that got fsync'ed
-			 * and never got linked before the fsync, skip it, as
-			 * replaying it is pointless since it would be deleted
-			 * later. We skip logging tmpfiles, but it's always
-			 * possible we are replaying a log created with a kernel
-			 * that used to log tmpfiles.
+			 * An inode with no links is either:
+			 *
+			 * 1) A tmpfile (O_TMPFILE) that got fsync'ed and never
+			 *    got linked before the fsync, skip it, as replaying
+			 *    it is pointless since it would be deleted later.
+			 *    We skip logging tmpfiles, but it's always possible
+			 *    we are replaying a log created with a kernel that
+			 *    used to log tmpfiles;
+			 *
+			 * 2) A non-tmpfile which got its last link deleted
+			 *    while holding an open fd on it and later got
+			 *    fsynced through that fd. We always log the
+			 *    parent inodes when inode->last_unlink_trans is
+			 *    set to the current transaction, so ignore all the
+			 *    inode items for this inode. We will delete the
+			 *    inode when processing the parent directory with
+			 *    replay_dir_deletes().
 			 */
 			if (btrfs_inode_nlink(eb, inode_item) == 0) {
 				wc->ignore_cur_inode = true;
 				continue;
 			} else {
 				wc->ignore_cur_inode = false;
 			}
+		}
+
+		/* Inode keys are done during the first stage. */
+		if (key.type == BTRFS_INODE_ITEM_KEY &&
+		    wc->stage == LOG_WALK_REPLAY_INODES) {
+			u32 mode;
+
 			ret = replay_xattr_deletes(trans, root, log, path, key.objectid);
 			if (ret)
 				break;