From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933630AbcCNHZH (ORCPT ); Mon, 14 Mar 2016 03:25:07 -0400 Received: from mx2.suse.de ([195.135.220.15]:55092 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754737AbcCNHY5 (ORCPT ); Mon, 14 Mar 2016 03:24:57 -0400 Date: Mon, 14 Mar 2016 08:22:34 +0100 From: Jan Kara To: Tejun Heo Cc: Jan Kara , Peter Chen , Alan Stern , florian@mickler.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, usb-storage@lists.one-eyed-alien.net, Jan Kara , jkosina@suse.cz Subject: Re: Freezable workqueue blocks non-freezable workqueue during the system resume process Message-ID: <20160314072234.GC5213@quack.suse.cz> References: <20160223032056.GB12256@shlinux2.ap.freescale.net> <20160224072430.GC15452@shlinux2.ap.freescale.net> <20160225220112.GM6092@mtj.duckdns.org> <20160226061920.GA17288@shlinux2.ap.freescale.net> <20160302160058.GA29826@mtj.duckdns.org> <20160303093310.GC2307@quack.suse.cz> <20160311175610.GL24046@htj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160311175610.GL24046@htj.duckdns.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 11-03-16 12:56:10, Tejun Heo wrote: > Hello, Jan. > > On Thu, Mar 03, 2016 at 10:33:10AM +0100, Jan Kara wrote: > > > Ugh... that's nasty. I wonder whether the right thing to do is making > > > writeback workers non-freezable. IOs are supposed to be blocked from > > > lower layer anyway. Jan, what do you think? > > > > Well no, at least currently IO is not blocked in lower layers AFAIK - for > > that you'd need to freeze block devices & filesystems and there are issues > > At least libata does and I think SCSI does too, but yeah, there > probably are drivers which depend on block layer blocking IOs, which > btw is a pretty fragile way to go about as upper layers might not be > the only source of activities. > > > with that (Jiri Kosina was the last one which was trying to make this work > > AFAIR). And I think you need to stop writeback (and generally any IO) to be > > generated so that it doesn't interact in a strange way with device drivers > > being frozen. So IMO until suspend freezes filesystems & devices properly > > you have to freeze writeback workqueue. > > I still think the right thing to do is plugging that block layer or > low level drivers. It's like we're trying to plug multiple sources > when we can plug the point where they come together anyway. I agree that freezing writeback workers is a workaround for real issues at best and ideally we shouldn't have to do that. But at least for now I had the impression that it is needed for suspend to work reasonably reliably. Honza -- Jan Kara SUSE Labs, CR