linux-kernel - Re: [PATCH] PM / suspend: move userspace freeze before disk sync

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Date:   Fri, 3 Sep 2021 11:17:55 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Sean Nyekjaer <sean@...nix.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Richard Weinberger <richard@....at>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>, linux-mtd@...ts.infradead.org
Subject: Re: [PATCH] PM / suspend: move userspace freeze before disk sync

Hi Sean,

sean@...nix.com wrote on Fri, 3 Sep 2021 10:17:51 +0200:

> On Thu, Sep 02, 2021 at 06:28:14PM +0200, Rafael J. Wysocki wrote:
> > On Wed, Sep 1, 2021 at 10:35 AM Sean Nyekjaer <sean@...nix.com> wrote:  
> > >
> > > This fixes an issue where data remains unwritten before suspend.  
> > 
> > Well, it doesn't make the issue go away, it just hides it for you and
> > it may very well expose it for someone else.  
> 
> OK
> 
> > 
> > In particular, note that you can compile the kernel with
> > CONFIG_SUSPEND_SKIP_SYNC set which makes it not sync at all during
> > system-wide suspend and this is a valid case expected to work.  It
> > looks like this case doesn't work for you.
> >   
> > > UBI tried to write data, before the mtd device had been unsuspended.  
> > 
> > Well, that's the real problem and it can happen regardless of whether
> > or not this patch is there.  
> 
> How to fix it then?
> We can't live with devices that bricks on unsuspend :/

We then need to focus on UBI/UBIFS implementation (Richard is currently
off), maybe there is more logic than just a basic retry to implement.

Thanks,
Miquèl