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

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Date:   Tue, 14 Nov 2017 11:31:37 +0800
From:   Yu Chen <yu.c.chen@...el.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     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>,
        Dan Williams <dan.j.williams@...el.com>,
        Yu Chen <yu.chen.surf@...il.com>, linux-xfs@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Regression/XFS/PM] Freeze tasks failed in xfsaild

On Mon, Nov 13, 2017 at 09:14:14PM +0100, Luis R. Rodriguez wrote:
> On Mon, Nov 13, 2017 at 06:31:39PM +0800, Yu Chen wrote:
> > The xfs-buf/dm-1 should be freezed according to
> > commit 8018ec083c72 ("xfs: mark all internal workqueues
> > as freezable"), thus a easier way might be have to revert
> > commit 18f1df4e00ce ("xfs: Make xfsaild freezeable
> > again") for now, after this reverting the xfsaild/dm-1
> > becomes non-freezable again, thus pm does not see this
> > thread - unless we find a graceful way to treat xfsaild/dm-1
> > as 'frozen' if it is waiting for an already 'frozen' task,
> > or if the filesystem freeze is added in.
> > 
> > Any comments would be much appreciated.
> 
> Reverting 18f1df4e00ce ("xfs: Make xfsaild freezeable again")
> would break the proper form of the kthread for it to be freezable.
> This "form" is not defined formally, and sadly its just a form
> learned throughout years over different kthreads in the kernel.
> 
> I'm also not convinced all our hibernation / suspend woes would be fixed by
> reverting this commit, its why I worked instead on formalizing a proper freeze
> / thaw, which a lot of filesystems already implement prior to system
> hibernation / suspend / resume [0].
> 
> I'll be respinning this series without the last patch, provided I'm able to
> ensure I don't need the ext[234] hack I did in that thread. Can you test the
> first 3 patches *only* on that series and seeing if that helps on your XFS
> front as well?
> 
> [0] https://lkml.kernel.org/r/20171003185313.1017-1-mcgrof@kernel.org
> 
>   Luis
Thanks for the comment Luis,
Yes, I agree the freezing of filesystem is a proper/thorough fix for such
kind issues, but as Dan said, it might be a little risky for us to
to deploy it on our products currently, unless it is in the
mainline/stable branch. Although the XFS issue might not be 100% reproducible,
we can help test the patch set while seeking for a lightweight 'fix'.
Thanks,
	Yu