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[209.85.220.65]) by mx.google.com with SMTPS id g3sor4537509qkl.132.2019.05.06.08.31.40 for (Google Transport Security); Mon, 06 May 2019 08:31:40 -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=FRIaQzP6; 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=/mMrXRGNFAUnlBanOG6lIKcQ2qXCGdgFD/lAGVp5Ijk=; b=FRIaQzP6E02iKd/LRHknHIfMWsLyZYkm7mpr7xtkI8lziTP9HO5aTcwhKoD1xeJl+l LJ5TWqUWRpPULfLDQ9x/PvLI5fli0XeL3MsSie5TvrfsMET3Gl/9HMhkwF9I6MGhefTC +gQHztuD1M1KJvNefAKO4hi80EI7Zmczpw9BRff78wgif9vAQD6UC77vsuLAYMTmC8ky PucMrqf1nYZa4O/5oYWE5H/aUL/nMIMP4kg02NZtu1kM9CcwNXJ8MGolpZcRcAF2l6fe NRtM3OQwINXRd/oH77hQYjy5vvN13HvU4vu1AbegJZQ9u58BrtL5QNj8ukEvJhpVB0yy 1IbQ== X-Google-Smtp-Source: APXvYqz67LjvUcpWVy+9a/kdXG2DHFPz1tKZL6bzzKYk6SLWXPGaCHybrhcqtu/dXg/05cYZG9tUGA== X-Received: by 2002:a37:6c84:: with SMTP id h126mr21101343qkc.168.1557156699748; Mon, 06 May 2019 08:31:39 -0700 (PDT) Received: from localhost ([2620:10d:c091:500::3:34f3]) by smtp.gmail.com with ESMTPSA id t55sm6952498qth.59.2019.05.06.08.31.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 06 May 2019 08:31:38 -0700 (PDT) Date: Mon, 6 May 2019 08:31:36 -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 v4 RESEND] fs/writeback: use rcu_barrier() to wait for inflight wb switches going into workqueue when umount Message-ID: <20190506153136.GM374014@devbig004.ftw2.facebook.com> References: <20190429024108.54150-1-jiufei.xue@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190429024108.54150-1-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 Mon, Apr 29, 2019 at 10:41:08AM +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 > Acked-by: Tejun Heo > Cc: stable@kernel.org Andrew, I think it'd probably be best to route this through -mm. Thanks! -- tejun