Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755102Ab1BRDdh (ORCPT ); Thu, 17 Feb 2011 22:33:37 -0500 Received: from cantor2.suse.de ([195.135.220.15]:44394 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751416Ab1BRDdg convert rfc822-to-8bit (ORCPT ); Thu, 17 Feb 2011 22:33:36 -0500 Date: Fri, 18 Feb 2011 14:33:25 +1100 From: NeilBrown To: Mike Snitzer Cc: Vivek Goyal , Jens Axboe , linux-kernel@vger.kernel.org Subject: Re: blk_throtl_exit taking q->queue_lock is problematic Message-ID: <20110218143325.5738e127@notabene.brown> In-Reply-To: References: <20110216183114.26a3613b@notabene.brown> <20110216155305.GC14653@redhat.com> <20110217113536.2bbf308e@notabene.brown> <20110217011029.GA6793@redhat.com> <20110217165501.47f3c26f@notabene.brown> <20110217165906.GE9075@redhat.com> <20110218134025.2a2e5bbb@notabene.brown> X-Mailer: Claws Mail 3.7.8 (GTK+ 2.20.1; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3173 Lines: 76 On Thu, 17 Feb 2011 22:19:52 -0500 Mike Snitzer wrote: > On Thu, Feb 17, 2011 at 9:40 PM, NeilBrown wrote: > > On Thu, 17 Feb 2011 11:59:06 -0500 Vivek Goyal wrote: > >> So if we do this change for performance reasons, it still makes sense > >> but doing this change because md provided a q->queue_lock and took away that > >> lock without notifying block layer hence we do this change, is still not > >> the right reason, IMHO. > > > > Well...I like that patch, as it makes my life easier.... > > > > But I agree that md is doing something wrong. ?Now that ->queue_lock is > > always initialised, it is wrong to leave it in a state where it not defined. > > > > So maybe I'll apply this (after testing it a bit. ?The only reason for taking > > the lock queue_lock in a couple of places is to silence some warnings. > > > > Thanks, > > NeilBrown > > > > > > diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c > > index a23ffa3..909282d 100644 > > --- a/drivers/md/raid1.c > > +++ b/drivers/md/raid1.c > > @@ -959,7 +961,9 @@ static int make_request(mddev_t *mddev, struct bio * bio) > > ? ? ? ? ? ? ? ?atomic_inc(&r1_bio->remaining); > > ? ? ? ? ? ? ? ?spin_lock_irqsave(&conf->device_lock, flags); > > ? ? ? ? ? ? ? ?bio_list_add(&conf->pending_bio_list, mbio); > > + ? ? ? ? ? ? ? spin_lock(mddev->queue->queue_lock); > > ? ? ? ? ? ? ? ?blk_plug_device(mddev->queue); > > + ? ? ? ? ? ? ? spin_unlock(mddev->queue->queue_lock); > > ? ? ? ? ? ? ? ?spin_unlock_irqrestore(&conf->device_lock, flags); > > ? ? ? ?} > > ? ? ? ?r1_bio_write_done(r1_bio, bio->bi_vcnt, behind_pages, behind_pages != NULL); > > Noticed an inconsistency, raid10.c's additional locking also protects > the bio_list_add() whereas raid1.c's doesn't. Seems the additional > protection in raid10 isn't needed? Correct - not needed at all. I put it there because it felt a little cleaner keeping the two 'lock's together like the two 'unlock's. Probably confusing though... My other though is to stop using the block-layer plugging altogether like I have in RAID5 (Which I needed to do to make it work with DM). Then I wouldn't need to touch queue_lock at all - very tempting. Thanks for the review. NeilBrown > > > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c > > index 3b607b2..60e6cb1 100644 > > --- a/drivers/md/raid10.c > > +++ b/drivers/md/raid10.c > > @@ -970,8 +972,10 @@ static int make_request(mddev_t *mddev, struct bio * bio) > > > > ? ? ? ? ? ? ? ?atomic_inc(&r10_bio->remaining); > > ? ? ? ? ? ? ? ?spin_lock_irqsave(&conf->device_lock, flags); > > + ? ? ? ? ? ? ? spin_lock(mddev->queue->queue_lock); > > ? ? ? ? ? ? ? ?bio_list_add(&conf->pending_bio_list, mbio); > > ? ? ? ? ? ? ? ?blk_plug_device(mddev->queue); > > + ? ? ? ? ? ? ? spin_unlock(mddev->queue->queue_lock); > > ? ? ? ? ? ? ? ?spin_unlock_irqrestore(&conf->device_lock, flags); > > ? ? ? ?} > > -- 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/