From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 28 May 2001 22:58:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 28 May 2001 22:58:47 -0400 Received: from zeus.kernel.org ([209.10.41.242]:17825 "EHLO zeus.kernel.org") by vger.kernel.org with ESMTP id ; Mon, 28 May 2001 22:58:39 -0400 Message-ID: <3B13092F.F8AC6E92@uow.edu.au> Date: Tue, 29 May 2001 12:27:59 +1000 From: Andrew Morton X-Mailer: Mozilla 4.76 [en] (X11; U; Linux 2.4.5-pre4 i686) X-Accept-Language: en MIME-Version: 1.0 To: Arthur Naseef CC: linux-kernel@vger.kernel.org Subject: Re: Kernel 2.2: tq_scheduler functions scheduling and waiting In-Reply-To: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Arthur Naseef wrote: > > All: > > I have been diagnosing kernel panics for over a week and I have > concerns with the use of tq_scheduler for which I was hoping I > could get some assistance. > > Is it considered acceptable for functions in the tq_scheduler > task list to call schedule? Is it acceptable for such functions > to wait on wait queues? What limitations exist? When a task wants to exit, it cleans up all its stuff, sets its state to TASK_ZOMBIE and then calls schedule(). The scheduler takes it off the runqueue and the task is never again executed. It's just a couple of stack pages which are waiting for someone in wait4() to release. But imagine what happens if the TASK_ZOMBIE task hits schedule() and finds a tq_scheduler task to run. And that task calls schedule(). In state TASK_ZOMBIE. Messy. At the very least, the schedule() call will never return. If the tq_scheduler task sets current->state to TASK_[UN]INTERRUPTIBLE (as it should) before calling schedule() then it has overwritten TASK_ZOMBIE and the task which is trying to exit has become magically resurrected. As far as I can tell, the "dead" task will run again, do the `fake_volatile' thing in do_exit() and try to go zombie again. It would be very interesting to change the test in schedule(): sti(); - if (tq_scheduler) + if (tq_scheduler && current->state != TASK_ZOMBIE) goto handle_tq_scheduler; It's all rather unpleasant, and tq_scheduler was killed in 2.4. I suggest you take a look at all the serial drivers in 2.4, see how I converted them to use schedule_task(). Someone kindly ported schedule_task() to 2.2.recent, so you should be able to use that in the same way. -