Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753608AbZLCIBd (ORCPT ); Thu, 3 Dec 2009 03:01:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751817AbZLCIBd (ORCPT ); Thu, 3 Dec 2009 03:01:33 -0500 Received: from mail-iw0-f171.google.com ([209.85.223.171]:59172 "EHLO mail-iw0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751341AbZLCIBc convert rfc822-to-8bit (ORCPT ); Thu, 3 Dec 2009 03:01:32 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=NqwsIa+xo+szBbr4OjqtdQyt9IrPQt+4LChGlA+rXtFAWNy+8l+tINXZDVdEL6WhHH 4u3CjBtkQ2ZBzzIWe6F4GBD/HkJdPnIMjKQ8zRl+dJwOnIHeKUwIl49sIYTGtxRKUpC3 +4hJOkfdnNjnBW/xC3kdgoI9VoDTARByZF+Hg= MIME-Version: 1.0 In-Reply-To: References: <563a732e0912022249y1e831c6cv7f2d5d376b8a5f63@mail.gmail.com> Date: Thu, 3 Dec 2009 16:01:38 +0800 Message-ID: <563a732e0912030001p11a9388o5efd836912e0cad9@mail.gmail.com> Subject: Re: Should we use preempt_disable() in sleep_on_common()? From: liu pf To: Dmitry Adamushko Cc: linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1841 Lines: 59 On Thu, Dec 3, 2009 at 3:57 PM, Dmitry Adamushko wrote: > 2009/12/3 liu pf : >> Hi: >> >> I am puzzled with the following scenario. Could anyone enlighten me? >> >> Thanks >> pfliu >> >> >> static long __sched >> sleep_on_common(wait_queue_head_t *q, int state, long timeout) >> { >>    unsigned long flags; >>    wait_queue_t wait; >> >>    init_waitqueue_entry(&wait, current); >> >>    __set_current_state(state); >> >>    ==========>suppose that after task A  set state=TASK_INTERRUPTIBLE >> , it is preempted by task B. >> >>    spin_lock_irqsave(&q->lock, flags); >> ............................................................... >> } >> >> asmlinkage void __sched schedule(void) >> { >> ....................................................................................................... >>    if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) { >>        if (unlikely(signal_pending_state(prev->state, prev))) >>            prev->state = TASK_RUNNING; >>        else >>            deactivate_task(rq, prev, 1); >>       =============>This will remove task A from rq, but there are no >> wait queue referring to A, so we lose A. >>        switch_count = &prev->nvcsw; >>    } > > In this case, (preempt_count() & PREEMPT_ACTIVE) == 1(see > preempt_schedule_irq() and other use-cases of PREEMPT_ACTIVE) so we > don't  enter this block. > > i.e. a preempted task stays on its queue (with state != TASK_RUNNING > but that doesn't really matter). > > > -- Dmitry > Thank you very much -- 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/