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authorYue Zhao <findns94@gmail.com>2023-03-06 18:41:36 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-03-29 02:20:13 +0300
commit82b3aa2681ca92421c4b508e7c390000273c53fe (patch)
treedb852c34eca4448da0a885d131021a3df12c1a25
parenteaf7b66b76f85ce340c50b76e482c6f91593b8b0 (diff)
downloadlinux-82b3aa2681ca92421c4b508e7c390000273c53fe.tar.xz
mm, memcg: Prevent memory.swappiness load/store tearing
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|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. All occurrences of memcg->swappiness and vm_swappiness are updated with [READ|WRITE]_ONCE. [findns94@gmail.com: v3] Link: https://lkml.kernel.org/r/20230308162555.14195-3-findns94@gmail.com 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>
-rw-r--r--include/linux/swap.h8
-rw-r--r--mm/memcontrol.c6
2 files changed, 7 insertions, 7 deletions
diff --git a/include/linux/swap.h b/include/linux/swap.h
index d5d0b54e90e8..bfc3b06b5f8f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -620,18 +620,18 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
/* 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
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 06821e5f7604..1b0112afcad3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4179,9 +4179,9 @@ static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
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;
}
@@ -5353,7 +5353,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
#endif
page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX);
if (parent) {
- memcg->swappiness = mem_cgroup_swappiness(parent);
+ WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent));
memcg->oom_kill_disable = parent->oom_kill_disable;
page_counter_init(&memcg->memory, &parent->memory);