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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 9B083C4646D for ; Sat, 11 Aug 2018 02:46:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 40ECF223FF for ; Sat, 11 Aug 2018 02:46:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 40ECF223FF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727324AbeHKFRa (ORCPT ); Sat, 11 Aug 2018 01:17:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:49792 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727093AbeHKFRa (ORCPT ); Sat, 11 Aug 2018 01:17:30 -0400 Received: from home.goodmis.org (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (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 BF3C7223FF; Sat, 11 Aug 2018 02:44:58 +0000 (UTC) Date: Fri, 10 Aug 2018 22:44:56 -0400 From: Steven Rostedt To: Jia-Ju Bai Cc: peterz@infradead.org, mingo@redhat.com, will.deacon@arm.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] kernel: locking: rtmutex: Fix a possible sleep-in-atomic-context bug in rt_mutex_handle_deadlock() Message-ID: <20180811024456.ykccnkbdrac4nbem@home.goodmis.org> References: <20180811023524.13845-1-baijiaju1990@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180811023524.13845-1-baijiaju1990@gmail.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 11, 2018 at 10:35:24AM +0800, Jia-Ju Bai wrote: > The driver may sleep with holding a spinlock. > > The function call paths (from bottom to top) in Linux-4.16 are: > > [FUNC] schedule > kernel/locking/rtmutex.c, 1223: > schedule in rt_mutex_handle_deadlock > kernel/locking/rtmutex.c, 1273: > rt_mutex_handle_deadlock in rt_mutex_slowlock > kernel/locking/rtmutex.c, 1249: > _raw_spin_lock_irqsave in rt_mutex_slowlock > > To fix the bug, the spinlock is released before schedule() and then acquired again. > This is found by my static analysis tool (DSAC). > > Signed-off-by: Jia-Ju Bai > --- > kernel/locking/rtmutex.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c > index 2823d4163a37..af03e162f812 100644 > --- a/kernel/locking/rtmutex.c > +++ b/kernel/locking/rtmutex.c > @@ -1205,7 +1205,7 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state, > } > > static void rt_mutex_handle_deadlock(int res, int detect_deadlock, > - struct rt_mutex_waiter *w) > + struct rt_mutex_waiter *w, struct rt_mutex *lock) > { > /* > * If the result is not -EDEADLOCK or the caller requested > @@ -1219,8 +1219,10 @@ static void rt_mutex_handle_deadlock(int res, int detect_deadlock, > */ > rt_mutex_print_deadlock(w); > while (1) { > + raw_spin_unlock_irq(&lock->wait_lock); > set_current_state(TASK_INTERRUPTIBLE); > schedule(); > + raw_spin_lock_irq(&lock->wait_lock); > } If you look at the code you will notice that it stops the task and never lets it continue. Ever. If we hit this path, it means we are in a deadlock scenario and will not make any forward progress. If anything, it should simply be: rt_mutex_print_deadlock(w); + /* We're not going anywhere, release the wait_lock */ + raw_spin_unlock_irq(&lock->wait_lock); while (1) { set_current_state(TASK_INTERRUPTIBLE); schedule(); } -- Steve > } > > @@ -1269,7 +1271,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, > if (unlikely(ret)) { > __set_current_state(TASK_RUNNING); > remove_waiter(lock, &waiter); > - rt_mutex_handle_deadlock(ret, chwalk, &waiter); > + rt_mutex_handle_deadlock(ret, chwalk, &waiter, lock); > } > > /* > -- > 2.17.0