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[209.85.220.65]) by mx.google.com with SMTPS id i81sor7676124yba.62.2019.06.05.12.51.26 for (Google Transport Security); Wed, 05 Jun 2019 12:51:26 -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=l3SHbq+t; 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=ADSrVTY729P8giks2VI3lL/ewrVA0y+ziy53/CJHjbI=; b=l3SHbq+tQMcR8JiOwkKI+rqmX8UZZye9PTtYe2D5QDQJbkEw4tn4YzYjfj1Avcsc8J cRSil6+QYDOrKQcFibXBl8KHBvqgfc+1gWOKhOe5AQUjTBRcaA3c9aZHM9gXxsy42Uaj XaKe/llBw2BCOk7t9sYKNJWXw59+a0I7dELeuw9kQpYWeGkMxRiRyXAcTSC6Y+L4A1hI 8NfTciR75XJzP+w3pQnIvURLV7LJhtCB6aKw4xvZuKpyq0I/nCGRAMJWlVW7ec6CpZJy ACUbqKujEVikDTF5Sng3n0OT3pwVrcF9Was5/ZEXf62lg8i+p7yOdy49gg/QBSLKQy/T wMSA== X-Google-Smtp-Source: APXvYqxszqUD/k5nU1g4wHGqDzn8YOE0ACTETUwVMD6KIg9ukVr7Jucv9S+W7J8xRSISnfIGsWcd/E7G53G2roOi1so= X-Received: by 2002:a25:7c05:: with SMTP id x5mr19854493ybc.358.1559764285452; Wed, 05 Jun 2019 12:51:25 -0700 (PDT) MIME-Version: 1.0 References: <20190605024454.1393507-1-guro@fb.com> <20190605024454.1393507-2-guro@fb.com> <20190605171355.GA10098@tower.DHCP.thefacebook.com> In-Reply-To: <20190605171355.GA10098@tower.DHCP.thefacebook.com> From: Shakeel Butt Date: Wed, 5 Jun 2019 12:51:14 -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 Wed, Jun 5, 2019 at 10:14 AM Roman Gushchin wrote: > > On Tue, Jun 04, 2019 at 09:35:02PM -0700, Shakeel Butt wrote: > > 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? > > It is independent, but let's keep it here to avoid merge conflicts. > > It has been so for a long time, and nobody complained, so I'm not sure > if we really need a stable backport. Do you have a different opinion? > Nah, it's fine as it is.