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[209.85.220.65]) by mx.google.com with SMTPS id 125sor2552725yby.89.2019.04.19.11.33.02 for (Google Transport Security); Fri, 19 Apr 2019 11:33:02 -0700 (PDT) Received-SPF: pass (google.com: domain of htejun@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=vKnIY9ql; spf=pass (google.com: domain of htejun@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=htejun@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=2l+yySfkbLjZ7A6AZC9+tOMoDXh431piIaB1MqjCE0s=; b=vKnIY9qlcjEO4/xDKBuqisY4tcwNmuKVqmCCvxrmrgFg/BrWrtslw026dmHPjKt8wS 4LVM9r4aXHdN2ms11Xc2uYNc1ZDRZcuugF886rirSgFnjYk+XrtDOr0jcGDN8Ou0v5p0 2/EIxdHhlD4MfJkcokn63HtB+oVXq8znFxW6UI2IKtAjc7WHfQqBkj/Gf3QGxYnPd/Mo LIc9FlMJw9M1tZt1pkq9nvNGVbPpdO1CB7HbO3dFBlLZQtBGT+QrTcPN6a0yBEGMOXU6 3kpRxeL5VYzfTbypmKGkQfsRJ44nBEy3Or1cSa9rOBpfKXk5yMlAPDj/5ikbY4sSiAUe H+vA== X-Google-Smtp-Source: APXvYqxTuWsfhu6f6r5ali0UF2xMpp1330DZSyg/0vvk0URbiRBgcdOt0kyrcOvQjDDarprKxwZZVQ== X-Received: by 2002:a25:858d:: with SMTP id x13mr4733139ybk.38.1555698782082; Fri, 19 Apr 2019 11:33:02 -0700 (PDT) Received: from localhost ([2620:10d:c091:180::2162]) by smtp.gmail.com with ESMTPSA id k123sm1811854ywa.57.2019.04.19.11.33.00 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Apr 2019 11:33:00 -0700 (PDT) Date: Fri, 19 Apr 2019 11:32:58 -0700 From: Tejun Heo To: Jiufei Xue Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, joseph.qi@linux.alibaba.com, bo.liu@linux.alibaba.com Subject: Re: [PATCH v3] fs/writeback: use rcu_barrier() to wait for inflight wb switches going into workqueue when umount Message-ID: <20190419183258.GI374014@devbig004.ftw2.facebook.com> References: <20190418020426.89259-1-jiufei.xue@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190418020426.89259-1-jiufei.xue@linux.alibaba.com> User-Agent: Mutt/1.5.21 (2010-09-15) 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 Thu, Apr 18, 2019 at 10:04:26AM +0800, Jiufei Xue wrote: > synchronize_rcu() didn't wait for call_rcu() callbacks, so inode wb > switch may not go to the workqueue after synchronize_rcu(). Thus > previous scheduled switches was not finished even flushing the > workqueue, which will cause a NULL pointer dereferenced followed below. > > VFS: Busy inodes after unmount of vdd. Self-destruct in 5 seconds. Have a nice day... > BUG: unable to handle kernel NULL pointer dereference at 0000000000000278 > [] evict+0xb3/0x180 > [] iput+0x1b0/0x230 > [] inode_switch_wbs_work_fn+0x3c0/0x6a0 > [] worker_thread+0x4e/0x490 > [] ? process_one_work+0x410/0x410 > [] kthread+0xe6/0x100 > [] ret_from_fork+0x39/0x50 > > Replace the synchronize_rcu() call with a rcu_barrier() to wait for all > pending callbacks to finish. And inc isw_nr_in_flight after call_rcu() > in inode_switch_wbs() to make more sense. > > Suggested-by: Tejun Heo > Signed-off-by: Jiufei Xue > Cc: stable@kernel.org Except for the documentation part that Andrew raised, Acked-by: Tejun Heo Thanks. -- tejun