linux-kernel - Re: [PATCH v4] PM: Support aborting sleep during filesystem sync

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Message-ID: <CAGETcx_Fn3AzZo7gNvJnPxy=CNHpqAviGdUrww++SGySuBcaZw@mail.gmail.com>
Date: Wed, 1 Oct 2025 15:12:38 -0700
From: Saravana Kannan <saravanak@...gle.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Samuel Wu <wusamuel@...gle.com>, Len Brown <lenb@...nel.org>, 
	Pavel Machek <pavel@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Danilo Krummrich <dakr@...nel.org>, kernel-team@...roid.com, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] PM: Support aborting sleep during filesystem sync

On Wed, Oct 1, 2025 at 11:22 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Wed, Oct 1, 2025 at 12:37 AM Samuel Wu <wusamuel@...gle.com> wrote:
> >
> > On Tue, Sep 30, 2025 at 11:51 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > >
> > > Hi,
> > >
> > > On Tue, Sep 30, 2025 at 8:30 PM Samuel Wu <wusamuel@...gle.com> wrote:
> > > >
> > > > Hi Rafael,
> > > >
> > > > Just a friendly ping on this patch. Please let me know if there's any
> > > > feedback or if you'd like me to make any changes.
> > >
> > > Have you seen https://lore.kernel.org/all/20250909065836.32534-1-tuhaowen@uniontech.com/
> > > ?
> > >
> > > If so, what do you think about it?
> >
> > I was following this chain
> > (https://lore.kernel.org/all/20250908024655.14636-1-tuhaowen@uniontech.com/),
> > where there is some ongoing discussion on converging the solution.
> >
> > Our changes aren't mutually exclusive, and tuhaowen can build changes
> > on top of ours, even indicating:
> > > I'm happy to work on this as a follow-up patch series after your changes land, or we could explore a unified solution that handles both scenarios.
>
> That's fair.
>
> > These patchsets don't negate each other, so could we decouple these
> > two patchsets since they address different issues?
>
> Well, I'm not sure if they are really different.  After all, this is
> all about avoiding having to wait on an excessively long filesystem
> sync during suspend.

No, it's different. We don't mind a long filesystem sync if we don't
have a need to abort a suspend. If it takes 25 seconds to sync the
filesystem but there's no need to abort it, that's totally fine. So,
this patch is just about allowing abort to happen without waiting for
file system sync to finish.

The other patch's requirement is to always abort if suspend takes 25
seconds (or whatever the timeout is). IIRC, in his case, it's because
of a bad disk or say a USB disk getting unplugged. I'm not convinced a
suspend timeout is the right thing to do, but I'm not going to nack
it. But to implement his requirement, he can put a patch on top of
ours where he sets a timer and then aborts suspends if it fires.

> I'm also not sure why it is being pursued to be honest.  Is setting
> /sys/power/sync_on_suspend to 0 not regarded as a viable option?

We do want to sync on every suspend. So, we don't want to turn it off
completely.

Thanks,
Saravana