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From: Alan Huang <mmpgouride@gmail.com>
To: kent.overstreet@linux.dev
Cc: linux-bcachefs@vger.kernel.org, Alan Huang <mmpgouride@gmail.com>
Subject: [PATCH] bcachefs: Fix subtraction underflow
Date: Mon, 27 Jan 2025 17:12:41 +0800	[thread overview]
Message-ID: <20250127091241.470892-1-mmpgouride@gmail.com> (raw)

When ancestor is less than IS_ANCESTOR_BITMAP, we would get an incorrect
result.

Signed-off-by: Alan Huang <mmpgouride@gmail.com>
---
 fs/bcachefs/snapshot.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/snapshot.c b/fs/bcachefs/snapshot.c
index c54091a28909..ede0b480e7d4 100644
--- a/fs/bcachefs/snapshot.c
+++ b/fs/bcachefs/snapshot.c
@@ -146,8 +146,9 @@ bool __bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
 		goto out;
 	}
 
-	while (id && id < ancestor - IS_ANCESTOR_BITMAP)
-		id = get_ancestor_below(t, id, ancestor);
+	if (likely(ancestor >= IS_ANCESTOR_BITMAP))
+		while (id && id < ancestor - IS_ANCESTOR_BITMAP)
+			id = get_ancestor_below(t, id, ancestor);
 
 	ret = id && id < ancestor
 		? test_ancestor_bitmap(t, id, ancestor)
-- 
2.47.0


             reply	other threads:[~2025-01-27  9:12 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-01-27  9:12 Alan Huang [this message]
2025-01-28  0:00 ` [PATCH] bcachefs: Fix subtraction underflow Kent Overstreet

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