Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752842AbaJBUNl (ORCPT ); Thu, 2 Oct 2014 16:13:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:8964 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751493AbaJBUNk (ORCPT ); Thu, 2 Oct 2014 16:13:40 -0400 Date: Thu, 2 Oct 2014 22:10:20 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Fengguang Wu , Jet Chen , Su Tao , Yuanhan Liu , LKP , linux-kernel@vger.kernel.org, Marcel Holtmann , Peter Hurley Subject: Re: [rfcomm_run] WARNING: CPU: 1 PID: 79 at kernel/sched/core.c:7156 __might_sleep() Message-ID: <20141002201020.GA8907@redhat.com> References: <20140930080228.GD9561@wfg-t540p.sh.intel.com> <20141002110927.GE2849@worktop.programming.kicks-ass.net> <20141002123150.GC6324@worktop.programming.kicks-ass.net> <20141002124247.GD6324@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141002124247.GD6324@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/02, Peter Zijlstra wrote: > > On Thu, Oct 02, 2014 at 02:31:50PM +0200, Peter Zijlstra wrote: > > @@ -2086,24 +2086,22 @@ static void rfcomm_kill_listener(void) > > > > static int rfcomm_run(void *unused) > > { > > + DEFINE_WAIT_FUNC(wait, woken_wake_function); > > BT_DBG(""); > > > > set_user_nice(current, -10); > > > > rfcomm_add_listener(BDADDR_ANY); > > > > - while (1) { > > - set_current_state(TASK_INTERRUPTIBLE); > > - > > - if (kthread_should_stop()) > > - break; > > + add_wait_queue(&rfcomm_wq, &wait); > > + while (!kthread_should_stop()) { > > > > /* Process stuff */ > > rfcomm_process_sessions(); > > > > - schedule(); > > + wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); > > } > > - __set_current_state(TASK_RUNNING); > > + remove_wait_queue(&rfcomm_wq, &wait); > > > > rfcomm_kill_listener(); > > > > Hmm, I think there's a problem there. If someone were to do > kthread_stop() before wait_woken() we'd not actually stop, because > wait_woken() doesn't test KTHREAD_SHOULD_STOP before calling schedule(). > > We can't unconditionally put a kthread_should_stop() in because > to_kthread() would explode on a !kthread. The other obvious solution is > adding a second function, something like wait_woken_or_stop(), but that > appears somewhat ugly to me. > > Oleg, do you see another solution? You know, I already thought about the patch below for other reasons, it can probably simplify other users of kthread_should_stop(). Because this way we can rely on the signal checks in schedule(). (Just in case, the patch is not complete, see TODO). As for rfcomm_run(), perhaps it can ise it too? set_kthread_wants_signal(true); add_wait_queue(&rfcomm_wq, &wait); for (;;) { // This is only possible if kthread_should_stop() == T if (signal_pending(current)) break; rfcomm_process_sessions(); wait_woken(TASK_INTERRUPTIBLE); } Of course, this assumes that rfcomm_process_sessions() can't do something "really bad" if signal_pending() is true. What do you think? Oleg. --- x/kernel/kthread.c +++ x/kernel/kthread.c @@ -49,6 +49,7 @@ struct kthread { enum KTHREAD_BITS { KTHREAD_IS_PER_CPU = 0, KTHREAD_SHOULD_STOP, + KTHREAD_WANTS_SIGNAL, KTHREAD_SHOULD_PARK, KTHREAD_IS_PARKED, }; @@ -442,6 +443,21 @@ int kthread_park(struct task_struct *k) return ret; } +void set_kthread_wants_signal(bool on) +{ + unsigned long *kflags = &to_kthread(current)->flags; + unsigned long irqflags; + + if (on) { + set_bit(KTHREAD_WANTS_SIGNAL, kflags); + } else { + spin_lock_irqsave(¤t->sighand->siglock, irqflags); + clear_bit(KTHREAD_WANTS_SIGNAL, kflags); + recalc_sigpending(); + spin_unlock_irqrestore(¤t->sighand->siglock, irqflags); + } +} + /** * kthread_stop - stop a thread created by kthread_create(). * @k: thread created by kthread_create(). @@ -469,6 +485,9 @@ int kthread_stop(struct task_struct *k) if (kthread) { set_bit(KTHREAD_SHOULD_STOP, &kthread->flags); __kthread_unpark(k, kthread); + // TODO: this is racy, we need ->siglock. + if (test_bit(KTHREAD_WANTS_SIGNAL, &to_kthread(k)->flags)) + set_tsk_thread_flag(k, TIF_SIGPENDING); wake_up_process(k); wait_for_completion(&kthread->exited); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/