Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754055AbdDEHci (ORCPT ); Wed, 5 Apr 2017 03:32:38 -0400 Received: from mx2.suse.de ([195.135.220.15]:49754 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751220AbdDEHch (ORCPT ); Wed, 5 Apr 2017 03:32:37 -0400 Date: Wed, 5 Apr 2017 09:32:33 +0200 From: Michal Hocko To: NeilBrown Cc: Jens Axboe , linux-block@vger.kernel.org, linux-mm@kvack.org, LKML , Ming Lei Subject: Re: [PATCH v2] loop: Add PF_LESS_THROTTLE to block/loop device thread. Message-ID: <20170405073233.GD6035@dhcp22.suse.cz> References: <871staffus.fsf@notabene.neil.brown.name> <87wpazh3rl.fsf@notabene.neil.brown.name> <20170405071927.GA7258@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170405071927.GA7258@dhcp22.suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1476 Lines: 45 On Wed 05-04-17 09:19:27, Michal Hocko wrote: > On Wed 05-04-17 14:33:50, NeilBrown wrote: [...] > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > > index 0ecb6461ed81..44b3506fd086 100644 > > --- a/drivers/block/loop.c > > +++ b/drivers/block/loop.c > > @@ -852,6 +852,7 @@ static int loop_prepare_queue(struct loop_device *lo) > > if (IS_ERR(lo->worker_task)) > > return -ENOMEM; > > set_user_nice(lo->worker_task, MIN_NICE); > > + lo->worker_task->flags |= PF_LESS_THROTTLE; > > return 0; > > As mentioned elsewhere, PF flags should be updated only on the current > task otherwise there is potential rmw race. Is this safe? The code runs > concurrently with the worker thread. I believe you need something like this instead --- diff --git a/drivers/block/loop.c b/drivers/block/loop.c index f347285c67ec..07b2a909e4fb 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -844,10 +844,16 @@ static void loop_unprepare_queue(struct loop_device *lo) kthread_stop(lo->worker_task); } +int loop_kthread_worker_fn(void *worker_ptr) +{ + current->flags |= PF_LESS_THROTTLE; + return kthread_worker_fn(worker_ptr); +} + static int loop_prepare_queue(struct loop_device *lo) { kthread_init_worker(&lo->worker); - lo->worker_task = kthread_run(kthread_worker_fn, + lo->worker_task = kthread_run(loop_kthread_worker_fn, &lo->worker, "loop%d", lo->lo_number); if (IS_ERR(lo->worker_task)) return -ENOMEM; -- Michal Hocko SUSE Labs