From: Michal Hocko <mhocko@suse.com> To: Yue Zhao <findns94@gmail.com> Cc: akpm@linux-foundation.org, roman.gushchin@linux.dev, hannes@cmpxchg.org, shakeelb@google.com, muchun.song@linux.dev, willy@infradead.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, tangyeechou@gmail.com Subject: Re: [PATCH v2, 2/4] mm, memcg: Prevent memory.swappiness load/store tearing Date: Mon, 6 Mar 2023 18:50:15 +0100 [thread overview] Message-ID: <ZAYn19jFPO9KR2Si@dhcp22.suse.cz> (raw) In-Reply-To: <20230306154138.3775-3-findns94@gmail.com> On Mon 06-03-23 23:41:36, Yue Zhao wrote: > 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. > > Signed-off-by: Yue Zhao <findns94@gmail.com> Acked-by: Michal Hocko <mhocko@suse.com> Thanks! > --- > include/linux/swap.h | 8 ++++---- > mm/memcontrol.c | 4 ++-- > 2 files changed, 6 insertions(+), 6 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 209a425739a9..3f3fe43d1766 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..dca895c66a9b 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; > } > -- > 2.17.1 -- Michal Hocko SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> To: Yue Zhao <findns94-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Cc: akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org, hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, muchun.song-fxUVXftIFDnyG1zEObXtfA@public.gmane.org, willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tangyeechou-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org Subject: Re: [PATCH v2, 2/4] mm, memcg: Prevent memory.swappiness load/store tearing Date: Mon, 6 Mar 2023 18:50:15 +0100 [thread overview] Message-ID: <ZAYn19jFPO9KR2Si@dhcp22.suse.cz> (raw) In-Reply-To: <20230306154138.3775-3-findns94-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> On Mon 06-03-23 23:41:36, Yue Zhao wrote: > 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. > > Signed-off-by: Yue Zhao <findns94-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Acked-by: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> Thanks! > --- > include/linux/swap.h | 8 ++++---- > mm/memcontrol.c | 4 ++-- > 2 files changed, 6 insertions(+), 6 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 209a425739a9..3f3fe43d1766 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..dca895c66a9b 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; > } > -- > 2.17.1 -- Michal Hocko SUSE Labs
next prev parent reply other threads:[~2023-03-06 17:51 UTC|newest] Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-03-06 15:41 [PATCH v2, 0/4] mm, memcg: cgroup v1 and v2 tunable load/store tearing fixes Yue Zhao 2023-03-06 15:41 ` Yue Zhao 2023-03-06 15:41 ` [PATCH v2, 1/4] mm, memcg: Prevent memory.oom.group load/store tearing Yue Zhao 2023-03-06 15:41 ` Yue Zhao 2023-03-06 17:47 ` Michal Hocko 2023-03-06 17:47 ` Michal Hocko 2023-03-06 15:41 ` [PATCH v2, 2/4] mm, memcg: Prevent memory.swappiness " Yue Zhao 2023-03-06 17:50 ` Michal Hocko [this message] 2023-03-06 17:50 ` Michal Hocko 2023-03-06 15:41 ` [PATCH v2, 3/4] mm, memcg: Prevent memory.oom_control " Yue Zhao 2023-03-06 15:41 ` Yue Zhao 2023-03-06 17:53 ` Michal Hocko 2023-03-06 17:53 ` Michal Hocko 2023-03-08 14:51 ` Martin Zhao 2023-03-08 14:51 ` Martin Zhao 2023-03-06 15:41 ` [PATCH v2, 4/4] mm, memcg: Prevent memory.soft_limit_in_bytes " Yue Zhao 2023-03-06 15:41 ` Yue Zhao 2023-03-06 17:55 ` Michal Hocko 2023-03-06 17:55 ` Michal Hocko 2023-03-06 16:25 ` [PATCH v2, 0/4] mm, memcg: cgroup v1 and v2 tunable load/store tearing fixes Shakeel Butt 2023-03-06 16:25 ` Shakeel Butt 2023-03-06 17:51 ` Roman Gushchin 2023-03-06 17:51 ` Roman Gushchin
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