linux-kernel - [PATCH AUTOSEL 5.4 2/3] btrfs: output extra debug info if we failed to find an inline backref

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Date:   Thu,  7 Sep 2023 11:44:22 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Qu Wenruo <wqu@...e.com>, David Sterba <dsterba@...e.com>,
        Sasha Levin <sashal@...nel.org>, clm@...com,
        josef@...icpanda.com, linux-btrfs@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 2/3] btrfs: output extra debug info if we failed to find an inline backref

From: Qu Wenruo <wqu@...e.com>

[ Upstream commit 7f72f50547b7af4ddf985b07fc56600a4deba281 ]

[BUG]
Syzbot reported several warning triggered inside
lookup_inline_extent_backref().

[CAUSE]
As usual, the reproducer doesn't reliably trigger locally here, but at
least we know the WARN_ON() is triggered when an inline backref can not
be found, and it can only be triggered when @insert is true. (I.e.
inserting a new inline backref, which means the backref should already
exist)

[ENHANCEMENT]
After the WARN_ON(), dump all the parameters and the extent tree
leaf to help debug.

Link: https://syzkaller.appspot.com/bug?extid=d6f9ff86c1d804ba2bc6
Signed-off-by: Qu Wenruo <wqu@...e.com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/btrfs/extent-tree.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index e47f53e780890..a9191a0d2f4c9 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -895,6 +895,11 @@ int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
 		err = -ENOENT;
 		goto out;
 	} else if (WARN_ON(ret)) {
+		btrfs_print_leaf(path->nodes[0]);
+		btrfs_err(fs_info,
+"extent item not found for insert, bytenr %llu num_bytes %llu parent %llu root_objectid %llu owner %llu offset %llu",
+			  bytenr, num_bytes, parent, root_objectid, owner,
+			  offset);
 		err = -EIO;
 		goto out;
 	}
-- 
2.40.1