Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756659Ab3FEQlG (ORCPT ); Wed, 5 Jun 2013 12:41:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:65345 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755761Ab3FEQlE (ORCPT ); Wed, 5 Jun 2013 12:41:04 -0400 Date: Wed, 5 Jun 2013 18:37:02 +0200 From: Oleg Nesterov To: Imre Deak Cc: Andrew Morton , Daniel Vetter , Dave Jones , David Howells , Jens Axboe , Linus Torvalds , Lukas Czerner , "Paul E. McKenney" , linux-kernel@vger.kernel.org Subject: Re: [PATCH] wait: fix false timeouts when using wait_event_timeout() Message-ID: <20130605163702.GA26135@redhat.com> References: <20130604192818.GA31316@redhat.com> <1370381717.8432.14.camel@ideak-mobl> <1370382051.8432.16.camel@ideak-mobl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1370382051.8432.16.camel@ideak-mobl> 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 Content-Length: 2790 Lines: 89 On 06/05, Imre Deak wrote: > > On Wed, 2013-06-05 at 00:35 +0300, Imre Deak wrote: > > On Tue, 2013-06-04 at 21:28 +0200, Oleg Nesterov wrote: > > > > > > Shouldn't we also change wait_event_timeout() ? Say, > > > > > > #define wait_event_timeout(wq, condition, timeout) \ > > > ({ \ > > > long __ret = timeout; \ > > > if (!(condition)) \ > > > __wait_event_timeout(wq, condition, __ret); \ > > > else if (!__ret) \ > > > __ret = 1; \ > > > __ret; \ > > > }) > > > > > > Or wait_event_timeout(timeout => 0) is not legal in a non-void context? > > > > > > To me the code like > > > > > > long wait_for_something(bool nonblock) > > > { > > > timeout = nonblock ? 0 : DEFAULT_TIMEOUT; > > > return wait_event_timeout(..., timeout); > > > } > > > > > > looks reasonable and correct. But it is not? > > > > I don't see why it would be not legal. Note though that in the above > > form wait_event_timeout(cond, 0) would still schedule() if cond is > > false, which is not what I'd expect from a non-blocking function. Yes, if false. But what if it is true? > Ah sorry, if you also rewrite __wait_event_timeout() then timeout=>0 > wouldn't schedule(), so things would work as expected. Can't understand... probably you missed my point. Let me try again. I think that wait_eveint_timeout(wq, COND, 0) should return !!(COND). But it doesn't, for example wait_event_timeout(wq, true, 0) == 0, this doesn'tlook right to me. And, this is off-topic, but wait_eveint_timeout/__wait_eveint_timeout do not match wait_event/__wait_event. IOW, you can't use __wait_eveint_timeout() if you do not need the fast-path check. So. How about #define __wait_event_timeout(wq, condition, timeout) \ ({ \ DEFINE_WAIT(__wait); \ long __ret = 0, __to = timeout; \ \ for (;;) { \ prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); \ if (condition) { \ __ret = __to ?: 1; \ break; \ } \ if (!__to) \ break; \ __to = schedule_timeout(__to); \ } \ finish_wait(&wq, &__wait); \ __ret; \ }) #define wait_event_timeout(wq, condition, timeout) \ ({ \ long __ret; \ if (condition) \ __ret = (timeout) ?: 1; \ else \ __ret = __wait_event_timeout(wq, condition, timeout); \ __ret; \ }) ? Othwerwise we should document the fact that the caller should alvays verify timeout != 0 if it checks the result of wait_event_timeout(). -- 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/