linux-kernel - [PATCH] mm/swapfile: mark racy access on si->highest

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Date: Sat, 27 Apr 2024 14:29:56 +0800
From: linke li <lilinke99@...com>
To: 
Cc: xujianhao01@...il.com,
	linke li <lilinke99@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] mm/swapfile: mark racy access on si->highest_bit

In scan_swap_map_slots(), si->highest_bit can by changed by
swap_range_alloc() concurrently. All reads on si->highest_bit except one
is either protected by lock or read using READ_ONCE. So mark the one racy
read on si->highest_bit as benign using READ_ONCE.

This patch is aimed at reducing the number of benign races reported by
KCSAN in order to focus future debugging effort on harmful races.

Signed-off-by: linke li <lilinke99@...com>
---
 mm/swapfile.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 556ff7347d5f..fb2243f7f06b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -854,7 +854,7 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
 		last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
 
 		/* Locate the first empty (unaligned) cluster */
-		for (; last_in_cluster <= si->highest_bit; offset++) {
+		for (; last_in_cluster <= READ_ONCE(si->highest_bit); offset++) {
 			if (si->swap_map[offset])
 				last_in_cluster = offset + SWAPFILE_CLUSTER;
 			else if (offset == last_in_cluster) {
-- 
2.39.3 (Apple Git-146)