From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423223AbWF1Ipu (ORCPT ); Wed, 28 Jun 2006 04:45:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1423224AbWF1Ipu (ORCPT ); Wed, 28 Jun 2006 04:45:50 -0400 Received: from smtp.osdl.org ([65.172.181.4]:35482 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1423223AbWF1Ipt (ORCPT ); Wed, 28 Jun 2006 04:45:49 -0400 Date: Wed, 28 Jun 2006 01:45:44 -0700 From: Andrew Morton To: Zou Nan hai Cc: mingo@elte.hu, linux-kernel@vger.kernel.org Subject: Re: [Patch] jbd commit code deadloop when installing Linux Message-Id: <20060628014544.198b9eb4.akpm@osdl.org> In-Reply-To: <1151477429.6052.42.camel@linux-znh> References: <1151470123.6052.17.camel@linux-znh> <20060627234005.dda13686.akpm@osdl.org> <20060628063859.GA9726@elte.hu> <20060627235500.8c2c290e.akpm@osdl.org> <1151473582.6052.28.camel@linux-znh> <20060628004029.efcc8a03.akpm@osdl.org> <1151474577.6052.33.camel@linux-znh> <20060628010422.dc73b7e9.akpm@osdl.org> <1151477429.6052.42.camel@linux-znh> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.17; i686-pc-linux-gnu) Mime-Version: 1.0 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 On 28 Jun 2006 14:50:29 +0800 Zou Nan hai wrote: > On Wed, 2006-06-28 at 16:04, Andrew Morton wrote: > > On 28 Jun 2006 14:02:57 +0800 > > Zou Nan hai wrote: > > > > > > > However I think cond_resched_lock and cond_resched_softirq also need fix > > > > > to make the semantic consistent. > > > > > > > > > > Please check the following patch. > > > > > > > > > > > > > Ah. I think the return value from these functions should mean "something > > > > disruptive happened", if you like. > > > > > > > > See, the callers of cond_resched_lock() aren't interested in whether > > > > cond_resched_lock() actually called schedule(). They want to know whether > > > > cond_resched_lock() dropped the lock. Because if the lock was dropped, the > > > > caller needs to take some special action, regardless of whether schedule() > > > > was finally called. > > > > > > > > So I think the patch I queued is OK, agree? > > > > > > I am afraid the code like cond_resched_lock check in > > > fs/jbd/checkpoint.c log_do_checkpoint may fall into endless retry in > > > some condition, will it? > > > > Oh crap, yes. If need_resched() and system_state==SYSTEM_BOOTING then > > cond_resched_lock() will drop the lock but won't schedule. So it'll return > > true but won't clear need_resched() and the caller will lock up. > > > > So if cond_resched_foo() ends up dropping the lock it _must_ call > > schedule() to clear need_resched(). > > > > So, how about this (it needs some code comments!) > > > > > > The patch works for the install test env. Thanks. > However I still have some concern on cond_resched_lock(), on an UP > kernel it will return 1 if schedule happen, but actually it does not > drop any lock, that semantic seems to be different to SMP kernel. That's OK (I think - I don't have a good track record in this thread). If the kernel is non-preemptible and UP, we want to return true from cond_resched_foo() if we called schedule(). Because schedule() might allow a different thread into the kernel which might modify the locked data. And if the kernel is preemptible and UP, we want to return true from cond_resched_foo() if we dropped the lock, because that internally does a preempt_enable(). And the patch (hopefully) satisfies those requirements. Does that all sound solid?