linux-kernel - Re: [Regression/XFS/PM] Freeze tasks failed in xfsaild

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Date:   Wed, 15 Nov 2017 08:25:38 +1100
From:   Dave Chinner <david@...morbit.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Yu Chen <yu.c.chen@...el.com>, Michal Hocko <mhocko@...e.com>,
        Hendrik Woltersdorf <hendrikw@...or.de>,
        Dave Chinner <dchinner@...hat.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jiri Kosina <jkosina@...e.cz>, Len Brown <len.brown@...el.com>,
        Rui Zhang <rui.zhang@...el.com>,
        Yu Chen <yu.chen.surf@...il.com>, linux-xfs@...r.kernel.org,
        Linux-pm mailing list <linux-pm@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Thorsten Leemhuis <linux@...mhuis.info>,
        oleg.b.antonyan@...il.com, Oliver Neukum <oneukum@...e.com>
Subject: Re: [Regression/XFS/PM] Freeze tasks failed in xfsaild

On Tue, Nov 14, 2017 at 09:19:15PM +0100, Luis R. Rodriguez wrote:
> This is another way to say suspend has been busted on XFS for a very long time,
> but I would not blame XFS -- this is a kernel issue to get proper filesystem
> suspend working right, and the way we currently deal with kthreads is just
> a sloppy goo mess which has created this situation.

Yes, and I've been telling people that suspend on journalling
filesystems has been broken for a long time (i.e since I first
realised the scope of the problem back in 2005). However, only XFS
triggers those conditions regularly because it is the most
asynchronous of the "freezable" journalling filesytems and has the
most reliance on co-ordination of kernel threads and workqueues to
function correctly.

IOWs, suspend of filesystems has been broken forever, and we've been
slapping bandaids on it in XFS forever. Now we've got to a
catch-22 situation that bandaids can't fix. We need structural
fixes, like I said we needed to do more than 10 years ago.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com