From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB93BC28EBD for ; Sun, 9 Jun 2019 16:56:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A492F204EC for ; Sun, 9 Jun 2019 16:56:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560099408; bh=3sIAlWKWwPUuJjwC0HO+q/XgjnhSqDSZGdpjme2YpkU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=DS7Z2EQrIEhgyWS/HQ4VZCWgop0GOwX94KUIhB7/LUsS9Am+FY0fWAob6Kt399DLE uEtMVW64nOqoCc6p8rjABoEvwN7HVBgURBvz9cnTFY6Cr/I0R98/rULBa2P6W+eOC2 K6Fl7MSRsuTnRI8drBX1lVnqwLpL1CMe1CzsAcYA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733048AbfFIQ4r (ORCPT ); Sun, 9 Jun 2019 12:56:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:59316 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732651AbfFIQ4k (ORCPT ); Sun, 9 Jun 2019 12:56:40 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6DC23205ED; Sun, 9 Jun 2019 16:56:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560099399; bh=3sIAlWKWwPUuJjwC0HO+q/XgjnhSqDSZGdpjme2YpkU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Cgp2TP5nJEckplASU2tbr0kP1+aslzj97ZmUkrz7z/EhHeDmoI4zjBvQ9TuCfZZ74 vumURT6afBRZJ/jwbqXMHVPCzTlozgNJFrPdXmebtrCfek+F8b3Ua2gAZ4sU/4B2Ln +6uFFw0uHXaL0Xb6k1uTmzkOSk9wfmoaT7XfYvfM= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jiufei Xue , Tejun Heo , Andrew Morton , Linus Torvalds Subject: [PATCH 4.4 028/241] fs/writeback.c: use rcu_barrier() to wait for inflight wb switches going into workqueue when umount Date: Sun, 9 Jun 2019 18:39:30 +0200 Message-Id: <20190609164148.590888517@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190609164147.729157653@linuxfoundation.org> References: <20190609164147.729157653@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jiufei Xue commit ec084de929e419e51bcdafaafe567d9e7d0273b7 upstream. 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. Link: http://lkml.kernel.org/r/20190429024108.54150-1-jiufei.xue@linux.alibaba.com Signed-off-by: Jiufei Xue Acked-by: Tejun Heo Suggested-by: Tejun Heo Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/fs-writeback.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -530,8 +530,6 @@ static void inode_switch_wbs(struct inod ihold(inode); isw->inode = inode; - atomic_inc(&isw_nr_in_flight); - /* * In addition to synchronizing among switchers, I_WB_SWITCH tells * the RCU protected stat update paths to grab the mapping's @@ -539,6 +537,9 @@ static void inode_switch_wbs(struct inod * Let's continue after I_WB_SWITCH is guaranteed to be visible. */ call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn); + + atomic_inc(&isw_nr_in_flight); + goto out_unlock; out_free: @@ -910,7 +911,11 @@ restart: void cgroup_writeback_umount(void) { if (atomic_read(&isw_nr_in_flight)) { - synchronize_rcu(); + /* + * Use rcu_barrier() to wait for all pending callbacks to + * ensure that all in-flight wb switches are in the workqueue. + */ + rcu_barrier(); flush_workqueue(isw_wq); } }