linux-kernel - [PATCH 5.15.y] btrfs: don't BUG_ON() when 0 reference count at btrfs_lookup_extent

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Message-ID: <20250509100139.3246547-1-jianqi.ren.cn@windriver.com>
Date: Fri, 9 May 2025 18:01:39 +0800
From: <jianqi.ren.cn@...driver.com>
To: <gregkh@...uxfoundation.org>, <stable@...r.kernel.org>
CC: <patches@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        <jianqi.ren.cn@...driver.com>, <clm@...com>, <josef@...icpanda.com>,
        <dsterba@...e.com>, <linux-btrfs@...r.kernel.org>, <wqu@...e.com>,
        <fdmanana@...e.com>
Subject: [PATCH 5.15.y] btrfs: don't BUG_ON() when 0 reference count at btrfs_lookup_extent_info()

From: Filipe Manana <fdmanana@...e.com>

[ Upstream commit 28cb13f29faf6290597b24b728dc3100c019356f ]

Instead of doing a BUG_ON() handle the error by returning -EUCLEAN,
aborting the transaction and logging an error message.

Reviewed-by: Qu Wenruo <wqu@...e.com>
Signed-off-by: Filipe Manana <fdmanana@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
[Minor conflict resolved due to code context change.]
Signed-off-by: Jianqi Ren <jianqi.ren.cn@...driver.com>
Signed-off-by: He Zhe <zhe.he@...driver.com>
---
Verified the build test
---
 fs/btrfs/extent-tree.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 551faae77bc3..8959506a0aa7 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -176,6 +176,14 @@ int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
 			ei = btrfs_item_ptr(leaf, path->slots[0],
 					    struct btrfs_extent_item);
 			num_refs = btrfs_extent_refs(leaf, ei);
+			if (unlikely(num_refs == 0)) {
+				ret = -EUCLEAN;
+				btrfs_err(fs_info,
+			"unexpected zero reference count for extent item (%llu %u %llu)",
+					  key.objectid, key.type, key.offset);
+				btrfs_abort_transaction(trans, ret);
+				goto out_free;
+			}
 			extent_flags = btrfs_extent_flags(leaf, ei);
 		} else {
 			ret = -EINVAL;
@@ -187,8 +195,6 @@ int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
 
 			goto out_free;
 		}
-
-		BUG_ON(num_refs == 0);
 	} else {
 		num_refs = 0;
 		extent_flags = 0;
@@ -218,10 +224,19 @@ int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
 			goto search_again;
 		}
 		spin_lock(&head->lock);
-		if (head->extent_op && head->extent_op->update_flags)
+		if (head->extent_op && head->extent_op->update_flags) {
 			extent_flags |= head->extent_op->flags_to_set;
-		else
-			BUG_ON(num_refs == 0);
+		} else if (unlikely(num_refs == 0)) {
+			spin_unlock(&head->lock);
+			mutex_unlock(&head->mutex);
+			spin_unlock(&delayed_refs->lock);
+			ret = -EUCLEAN;
+			btrfs_err(fs_info,
+			  "unexpected zero reference count for extent %llu (%s)",
+				  bytenr, metadata ? "metadata" : "data");
+			btrfs_abort_transaction(trans, ret);
+			goto out_free;
+		}
 
 		num_refs += head->ref_mod;
 		spin_unlock(&head->lock);
-- 
2.34.1