+ mm-swapfile-mark-racy-access-on-si-highest_bit.patch added to mm-unstable branch

+ mm-swapfile-mark-racy-access-on-si-highest_bit.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/swapfile: mark racy access on si->highest_bit
has been added to the -mm mm-unstable branch.  Its filename is
     mm-swapfile-mark-racy-access-on-si-highest_bit.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swapfile-mark-racy-access-on-si-highest_bit.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: linke li <lilinke99@qq.com>
Subject: mm/swapfile: mark racy access on si->highest_bit
Date: Sat, 27 Apr 2024 14:29:56 +0800

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.

Link: https://lkml.kernel.org/r/tencent_912BC3E8B0291DA4A0028AB424076375DA07@qq.com
Signed-off-by: linke li <lilinke99@qq.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/swapfile.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/swapfile.c~mm-swapfile-mark-racy-access-on-si-highest_bit
+++ a/mm/swapfile.c
@@ -902,7 +902,7 @@ static int scan_swap_map_slots(struct sw
 		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) {
_

Patches currently in -mm which might be from lilinke99@qq.com are

mm-swapfile-mark-racy-access-on-si-highest_bit.patch