linux-kernel - [PATCH] xarray: Add a BUG_ON() to ensure caller is not sibling

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Message-Id: <20250528113124.87084-1-dev.jain@arm.com>
Date: Wed, 28 May 2025 17:01:24 +0530
From: Dev Jain <dev.jain@....com>
To: akpm@...ux-foundation.org,
	willy@...radead.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	david@...hat.com,
	anshuman.khandual@....com,
	ryan.roberts@....com,
	Dev Jain <dev.jain@....com>
Subject: [PATCH] xarray: Add a BUG_ON() to ensure caller is not sibling

Suppose xas is pointing somewhere near the end of the multi-entry batch.
Then it may happen that the computed slot already falls beyond the batch,
thus breaking the loop due to !xa_is_sibling(), and computing the wrong
order. Thus ensure that the caller is aware of this by triggering a BUG
when the entry is a sibling entry.

This patch is motivated by code inspection and not a real bug report.

Signed-off-by: Dev Jain <dev.jain@....com>
---
The patch applies on 6.15 kernel.

 lib/xarray.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/xarray.c b/lib/xarray.c
index 9644b18af18d..0f699766c24f 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1917,6 +1917,8 @@ int xas_get_order(struct xa_state *xas)
 	if (!xas->xa_node)
 		return 0;
 
+	XA_NODE_BUG_ON(xas->xa_node, xa_is_sibling(xa_entry(xas->xa,
+		       xas->xa_node, xas->xa_offset)));
 	for (;;) {
 		unsigned int slot = xas->xa_offset + (1 << order);
 
-- 
2.30.2