Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755895Ab1CGTlN (ORCPT ); Mon, 7 Mar 2011 14:41:13 -0500 Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:33523 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755820Ab1CGTlM (ORCPT ); Mon, 7 Mar 2011 14:41:12 -0500 Message-ID: <4D7534D6.7020000@kernel.dk> Date: Mon, 07 Mar 2011 20:41:10 +0100 From: Jens Axboe MIME-Version: 1.0 To: Jeff Moyer CC: Tejun Heo , Mike Snitzer , Jan Beulich , "David S. Miller" , linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org Subject: Re: [PATCH v2.6.38-rc5 2/2] block: blk-flush shouldn't call directly into q->request_fn() __blk_run_queue() References: <20110217111511.GQ19830@htj.dyndns.org> <20110217111619.GR19830@htj.dyndns.org> <20110218094903.GF21209@htj.dyndns.org> <4D6E4A46.1040709@kernel.dk> <20110304182507.GY20499@htj.dyndns.org> <4D7533B1.3070308@kernel.dk> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2926 Lines: 71 On 2011-03-07 20:39, Jeff Moyer wrote: > Jens Axboe writes: > >> On 2011-03-07 20:33, Jeff Moyer wrote: >>> Tejun Heo writes: >>> >>>> Hello, Jens. >>>> >>>> On Wed, Mar 02, 2011 at 08:46:46AM -0500, Jens Axboe wrote: >>>>>> Right, thanks. Jens, after you apply the two fixes for 2.6.38, I can >>>>>> create a merge branch for for-2.6.39/core which you can pull. Would >>>>>> that work for you? >>>>> >>>>> Thanks, that would be great. I'm applying them now. >>>> >>>> Okay, please pull from the following branch to receive the merge >>>> between linux-2.6-block:for-linus and :for-2.6.39/core. >>>> >>>> git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git block-for-2.6.39-core >>>> >>>> HEAD is e83a46bbb1d4c03defd733a64b727632a40059ad but git.korg seems a >>>> bit slow to sync, so if you don't see the commit there, please pull >>>> from master.korg. >>>> >>>> ssh://master.kernel.org/pub/scm/linux/kernel/git/tj/misc.git block-for-2.6.39-core >>>> >>>> Thanks. >>> >>> I know I'm coming to the party late (and maybe wrong), but I've got some >>> questions here. >>> >>> Tejun, you introduced a commit to the ide driver that made it block in >>> its request function. As far as I know, that's not allowed. For scsi, >>> at least, it has always allowed calling back into the request function >>> from the completion handler, and I think this is actully the common case >>> (not some corner case). >>> >>> So, why doesn't the ide driver see calls back into its request function >>> from the completion handler? It's clear that it calls blk_end_request >>> from ide_end_rq, which can definitely call __blk_run_queue. In other >>> words, why is it that the flush requests are triggerring this problem >>> while normal I/O isn't? >>> >>> I think the real issue may just be that the ide driver is blocking in >>> its request function. What have I missed? >> >> So the only case where the request_fn is called and you cannot block, is >> if you call it from your completion function. Any other invocation >> should be from process context. As long as you remember to drop the >> queue lock and re-enable interrupts, it should work. It's not great >> style and I would not recommend it for a performance environment, but it >> should work. > > So are you agreeing with me or disagreeing? ;-) It sounds to me like > you're saying that the ide driver should be able to cope with being > called from softirq context. I'm just stating how it should work :-) But yes, it sounds like IDE is violating this rule and that's why it was broken. Even with that, having explicit control of the queue running does make sense. -- Jens Axboe -- 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/