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

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

[Andrew Morton]

The patch titled
     Subject: mm, memcg: Prevent memory.swappiness load/store tearing
has been added to the -mm mm-unstable branch.  Its filename is
     mm-memcg-prevent-memoryswappiness-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-memoryswappiness-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.swappiness load/store tearing
Date: Mon, 6 Mar 2023 23:41:36 +0800

The knob for cgroup v1 memory controller: memory.swappiness
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->swappiness and vm_swappiness is lockless,
so both of them can be concurrently set at the same time
as we are trying to read them.

Link: https://lkml.kernel.org/r/20230306154138.3775-3-findns94@gmail.com
Signed-off-by: Yue Zhao <findns94@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.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: Muchun Song <muchun.song@linux.dev>
Cc: Tang Yizhou <tangyeechou@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/include/linux/swap.h~mm-memcg-prevent-memoryswappiness-load-store-tearing
+++ a/include/linux/swap.h
@@ -620,18 +620,18 @@ static inline int mem_cgroup_swappiness(
 {
 	/* Cgroup2 doesn't have per-cgroup swappiness */
 	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
-		return vm_swappiness;
+		return READ_ONCE(vm_swappiness);
 
 	/* root ? */
 	if (mem_cgroup_disabled() || mem_cgroup_is_root(memcg))
-		return vm_swappiness;
+		return READ_ONCE(vm_swappiness);
 
-	return memcg->swappiness;
+	return READ_ONCE(memcg->swappiness);
 }
 #else
 static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 {
-	return vm_swappiness;
+	return READ_ONCE(vm_swappiness);
 }
 #endif
 
--- a/mm/memcontrol.c~mm-memcg-prevent-memoryswappiness-load-store-tearing
+++ a/mm/memcontrol.c
@@ -4179,9 +4179,9 @@ static int mem_cgroup_swappiness_write(s
 		return -EINVAL;
 
 	if (!mem_cgroup_is_root(memcg))
-		memcg->swappiness = val;
+		WRITE_ONCE(memcg->swappiness, val);
 	else
-		vm_swappiness = val;
+		WRITE_ONCE(vm_swappiness, val);
 
 	return 0;
 }
_

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