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

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

[Andrew Morton]

The patch titled
     Subject: mm, memcg: Prevent memory.oom_control load/store tearing
has been added to the -mm mm-unstable branch.  Its filename is
     mm-memcg-prevent-memoryoom_control-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-memoryoom_control-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.oom_control load/store tearing
Date: Mon, 6 Mar 2023 23:41:37 +0800

The knob for cgroup v1 memory controller: memory.oom_control
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->oom_kill_disable 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/20230306154138.3775-4-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-memoryoom_control-load-store-tearing
+++ a/mm/memcontrol.c
@@ -4515,7 +4515,7 @@ static int mem_cgroup_oom_control_read(s
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_seq(sf);
 
-	seq_printf(sf, "oom_kill_disable %d\n", memcg->oom_kill_disable);
+	seq_printf(sf, "oom_kill_disable %d\n", READ_ONCE(memcg->oom_kill_disable));
 	seq_printf(sf, "under_oom %d\n", (bool)memcg->under_oom);
 	seq_printf(sf, "oom_kill %lu\n",
 		   atomic_long_read(&memcg->memory_events[MEMCG_OOM_KILL]));
@@ -4531,7 +4531,7 @@ static int mem_cgroup_oom_control_write(
 	if (mem_cgroup_is_root(memcg) || !((val == 0) || (val == 1)))
 		return -EINVAL;
 
-	memcg->oom_kill_disable = val;
+	WRITE_ONCE(memcg->oom_kill_disable, val);
 	if (!val)
 		memcg_oom_recover(memcg);
 
_

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