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Subject[PATCH] mm/swapfile: mark racy access on si->highest_bit
Date
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@qq.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)

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