From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755274Ab1IBHGc (ORCPT ); Fri, 2 Sep 2011 03:06:32 -0400 Received: from mail-ww0-f44.google.com ([74.125.82.44]:37403 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751482Ab1IBHGa (ORCPT ); Fri, 2 Sep 2011 03:06:30 -0400 Message-ID: <4E608081.5000107@gmail.com> Date: Fri, 02 Sep 2011 15:06:41 +0800 From: Shan Hai User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.18) Gecko/20110617 Thunderbird/3.1.11 MIME-Version: 1.0 To: Yong Zhang CC: sifram rajas , linux-kernel@vger.kernel.org Subject: Re: General question about TASK_INTERRUPTIBLE and schedule_timeout() References: <20110901020947.GA9096@zhy> <4E607523.30907@gmail.com> In-Reply-To: <4E607523.30907@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/02/2011 02:18 PM, Shan Hai wrote: > On 09/01/2011 10:09 AM, Yong Zhang wrote: >> On Wed, Aug 31, 2011 at 06:18:19PM +0530, sifram rajas wrote: >>> Hi, >>> >>> I have a general question about the following 2 lines of code I see >>> all over the kernel: >>> 1 set_current_state(TASK_INTERRUPTIBLE) ; >>> 2 schedule_timeout(); >>> >>> In the above code, if we encounter an interrupt after executing line >>> 1, we will end up >>> call schedule() from the architecture specific code for CONFIG_PREEMPT >>> kernels, after >>> the interrupt handler has been invokled. >> Yes. >> >>> This will cause the current task to sleep interruptibly forever > > Actually, sleeping forever in the TASK_INTERRUPTIBLE state is not > correct, > because even though the task is preempted by higher priority one > it will finally get a chance to run, but you will get time out value > of + preemption latency. > >>> instead of for a certain timeout interval. >> No. >> >> schedule() will not put an preempted task to sleep, see: > > This might be problematic, because on the IRQ to preemption check path > the PREEMPT_ACTIVE was already set and the following 'if' statement > could not hold because of > !(preempt_count() & PREEMPT_ACTIVE) == false > > and the pick_next_task() might put the preempted task to sleep. > I mean when the state of task is TASK_INTERRUPTIBLE the preempted task will be put to sleep, its true in sifram's case. Yong is right on stating "schedule() will not put an preempted task to sleep", its true for the task state of which is TASK_RUNNING. Cheers Shan Hai > Correct me on any misunderstanding :-) > > Cheers > Shan Hai > >> asmlinkage void __sched schduule(void) >> { >> ... >> if (prev->state&& !(preempt_count()& PREEMPT_ACTIVE)) { >> if (unlikely(signal_pending_state(prev->state, >> prev))) { >> prev->state = TASK_RUNNING; >> } else { >> ... >> } >> } >> ... >> } >> >> Thanks, >> Yong >> >>> Won't this defeat the purpose of the above code to schedule out or >>> sleep for a certain finite timeout ? >>> If yes, then what are the techniques to solve this problem ? >>> >>> >>> Thanks, >>> Sifram. >>> -- >>> 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/ >