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[209.85.220.65]) by mx.google.com with SMTPS id a8sor9416829ybc.119.2019.06.04.21.35.14 for (Google Transport Security); Tue, 04 Jun 2019 21:35:14 -0700 (PDT) Received-SPF: pass (google.com: domain of shakeelb@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=l6etWU3h; spf=pass (google.com: domain of shakeelb@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=EiZjBZHC5Luc27kYIuZtZXOYiqvfneCugvkG3Zxzj+0=; b=l6etWU3hoAIzk502NCLzqzCwueHjUuAnf/eR/wuiZbG2FPIk0eHDh2w2W5nSiNQHEq yUf6WkAw/xmU45plNLxfP6qOhMt0ugZl9MoJ8xIDlaCWNsHoct8OGKM/PKs61uNe3pPZ aIscz2/I4HZncJ6NXVBtM0ugZJlklYIwDqHhbISCJNKhl0MNuXwsRXEQbntjyqDTFqd0 Lk8t0r90YIAdrU2QKZzfq0ofEgZnHL22HS/F2/jiThl65tNXqWA69ZpWgKUW+PUUDna2 ExMgFaz75HDTB0wHox6aUC5wAp8HAFCKs/DTCOZRynpNNf6VylThXCEwBBXdNvFIgtgZ QkHQ== X-Google-Smtp-Source: APXvYqwYEsTxKXLhDDZZLM7bg5/6GEAiuuqGq8PUklt7d0KxCckL9NGG4Q/b5VxneyZkVXRh6FDzTj9EDbju++v3JZk= X-Received: by 2002:a25:943:: with SMTP id u3mr17294262ybm.293.1559709313724; Tue, 04 Jun 2019 21:35:13 -0700 (PDT) MIME-Version: 1.0 References: <20190605024454.1393507-1-guro@fb.com> <20190605024454.1393507-2-guro@fb.com> In-Reply-To: <20190605024454.1393507-2-guro@fb.com> From: Shakeel Butt Date: Tue, 4 Jun 2019 21:35:02 -0700 Message-ID: Subject: Re: [PATCH v6 01/10] mm: add missing smp read barrier on getting memcg kmem_cache pointer To: Roman Gushchin Cc: Andrew Morton , Linux MM , LKML , Kernel Team , Johannes Weiner , Vladimir Davydov , Waiman Long Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jun 4, 2019 at 7:45 PM Roman Gushchin wrote: > > Johannes noticed that reading the memcg kmem_cache pointer in > cache_from_memcg_idx() is performed using READ_ONCE() macro, > which doesn't implement a SMP barrier, which is required > by the logic. > > Add a proper smp_rmb() to be paired with smp_wmb() in > memcg_create_kmem_cache(). > > The same applies to memcg_create_kmem_cache() itself, > which reads the same value without barriers and READ_ONCE(). > > Suggested-by: Johannes Weiner > Signed-off-by: Roman Gushchin Reviewed-by: Shakeel Butt This seems like independent to the series. Shouldn't this be Cc'ed stable? > --- > mm/slab.h | 1 + > mm/slab_common.c | 3 ++- > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/slab.h b/mm/slab.h > index 739099af6cbb..1176b61bb8fc 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -260,6 +260,7 @@ cache_from_memcg_idx(struct kmem_cache *s, int idx) > * memcg_caches issues a write barrier to match this (see > * memcg_create_kmem_cache()). > */ > + smp_rmb(); > cachep = READ_ONCE(arr->entries[idx]); > rcu_read_unlock(); > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 58251ba63e4a..8092bdfc05d5 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -652,7 +652,8 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg, > * allocation (see memcg_kmem_get_cache()), several threads can try to > * create the same cache, but only one of them may succeed. > */ > - if (arr->entries[idx]) > + smp_rmb(); > + if (READ_ONCE(arr->entries[idx])) > goto out_unlock; > > cgroup_name(css->cgroup, memcg_name_buf, sizeof(memcg_name_buf)); > -- > 2.20.1 >