+ mm-memcg-prevent-memorysoft_limit_in_bytes-load-store-tearing.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm, memcg: Prevent memory.soft_limit_in_bytes load/store tearing
has been added to the -mm mm-unstable branch.  Its filename is
     mm-memcg-prevent-memorysoft_limit_in_bytes-load-store-tearing.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-prevent-memorysoft_limit_in_bytes-load-store-tearing.patch

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

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------------------------------------------------------
From: Yue Zhao <findns94@gmail.com>
Subject: mm, memcg: Prevent memory.soft_limit_in_bytes load/store tearing
Date: Mon, 6 Mar 2023 23:41:38 +0800

The knob for cgroup v1 memory controller: memory.soft_limit_in_bytes
is not protected by any locking so it can be modified while it is used.
This is not an actual problem because races are unlikely.
But it is better to use READ_ONCE/WRITE_ONCE to prevent compiler from
doing anything funky.

The access of memcg->soft_limit is lockless,
so it can be concurrently set at the same time as we are
trying to read it.

Link: https://lkml.kernel.org/r/20230306154138.3775-5-findns94@gmail.com
Signed-off-by: Yue Zhao <findns94@gmail.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tang Yizhou <tangyeechou@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/mm/memcontrol.c~mm-memcg-prevent-memorysoft_limit_in_bytes-load-store-tearing
+++ a/mm/memcontrol.c
@@ -3728,7 +3728,7 @@ static u64 mem_cgroup_read_u64(struct cg
 	case RES_FAILCNT:
 		return counter->failcnt;
 	case RES_SOFT_LIMIT:
-		return (u64)memcg->soft_limit * PAGE_SIZE;
+		return (u64)READ_ONCE(memcg->soft_limit) * PAGE_SIZE;
 	default:
 		BUG();
 	}
@@ -3870,7 +3870,7 @@ static ssize_t mem_cgroup_write(struct k
 		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
 			ret = -EOPNOTSUPP;
 		} else {
-			memcg->soft_limit = nr_pages;
+			WRITE_ONCE(memcg->soft_limit, nr_pages);
 			ret = 0;
 		}
 		break;
_

Patches currently in -mm which might be from findns94@gmail.com are

mm-memcg-prevent-memoryoomgroup-load-store-tearing.patch
mm-memcg-prevent-memoryswappiness-load-store-tearing.patch
mm-memcg-prevent-memoryoom_control-load-store-tearing.patch
mm-memcg-prevent-memorysoft_limit_in_bytes-load-store-tearing.patch