From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from www262.sakura.ne.jp ([202.181.97.72]:57850 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1032474AbeE0CWz (ORCPT ); Sat, 26 May 2018 22:22:55 -0400 Subject: [PATCH] bdi: Fix another oops in wb_workfn() To: syzbot , syzkaller-bugs@googlegroups.com, jack@suse.cz Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, axboe@kernel.dk, tj@kernel.org, david@fromorbit.com, linux-block@vger.kernel.org References: <000000000000cbd959056d1851ca@google.com> <0c7c5dea-7312-8a59-9d1b-5467f69719bf@I-love.SAKURA.ne.jp> From: Tetsuo Handa Message-ID: <314ae2e0-c873-04ce-9cd5-fe2acadaee26@I-love.SAKURA.ne.jp> Date: Sun, 27 May 2018 11:21:25 +0900 MIME-Version: 1.0 In-Reply-To: <0c7c5dea-7312-8a59-9d1b-5467f69719bf@I-love.SAKURA.ne.jp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org List-ID: >>From 8a8222698163d1fe180258566e9a3ff43f54fcd9 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Sun, 27 May 2018 11:08:20 +0900 Subject: [PATCH] bdi: Fix another oops in wb_workfn() syzbot is still hitting NULL pointer dereference at wb_workfn() [1]. This might be because we overlooked that delayed_work_timer_fn() does not check WB_registered before calling __queue_work() while mod_delayed_work() does not wait for already started delayed_work_timer_fn() because it uses del_timer() rather than del_timer_sync(). Make wb_shutdown() be careful about wb_wakeup_delayed() path. [1] https://syzkaller.appspot.com/bug?id=e0818ccb7e46190b3f1038b0c794299208ed4206 Signed-off-by: Tetsuo Handa Reported-by: syzbot Cc: Tejun Heo Cc: Dave Chinner Cc: Jan Kara Cc: Jens Axboe --- mm/backing-dev.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 7441bd9..31e1d7e 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -372,11 +372,24 @@ static void wb_shutdown(struct bdi_writeback *wb) cgwb_remove_from_bdi_list(wb); /* + * mod_delayed_work() is not appropriate here, for + * delayed_work_timer_fn() from wb_wakeup_delayed() does not check + * WB_registered before calling __queue_work(). + */ + del_timer_sync(&wb->dwork.timer); + /* + * Clear WORK_STRUCT_PENDING_BIT in order to make sure that next + * queue_delayed_work() actually enqueues this work to the tail, for + * wb_wakeup_delayed() already set WORK_STRUCT_PENDING_BIT before + * scheduling delayed_work_timer_fn(). + */ + cancel_delayed_work_sync(&wb->dwork); + /* * Drain work list and shutdown the delayed_work. !WB_registered * tells wb_workfn() that @wb is dying and its work_list needs to * be drained no matter what. */ - mod_delayed_work(bdi_wq, &wb->dwork, 0); + queue_delayed_work(bdi_wq, &wb->dwork, 0); flush_delayed_work(&wb->dwork); WARN_ON(!list_empty(&wb->work_list)); /* -- 1.8.3.1