linux-kernel - Re: [PATCH v5] PM: Support aborting sleep during filesystem sync

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Message-ID: <CAG2KctpHA+L=xh-VQ8SVDSRcqyL+ch=WMVrKS+pckLmC6uJwvw@mail.gmail.com>
Date: Tue, 21 Oct 2025 13:13:39 -0700
From: Samuel Wu <wusamuel@...gle.com>
To: Hillf Danton <hdanton@...a.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@...nel.org>, Len Brown <lenb@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, kernel-team@...roid.com, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] PM: Support aborting sleep during filesystem sync

On Fri, Oct 17, 2025 at 5:17 PM Hillf Danton <hdanton@...a.com> wrote:
>
> On Fri, 17 Oct 2025 23:39:06 +0000 Samuel Wu wrote:
> > +/**
> > + * pm_sleep_fs_sync - Trigger fs_sync with ability to abort
> > + *
> > + * Return 0 on successful file system sync, otherwise returns -EBUSY if file
> > + * system sync was aborted.
> > + */
> > +int pm_sleep_fs_sync(void)
> > +{
> > +     bool need_pm_sleep_fs_sync_requeue;
> > +     unsigned long flags;
> > +
> > +     do {
> > +             spin_lock_irqsave(&pm_sleep_fs_sync_lock, flags);
> > +             reinit_completion(&pm_sleep_fs_sync_complete);
>
> Given difficulty following up here, can you specify why reinit is needed?

There are two possibilities that make reinit_completion() necessary:
1. Suspend abort triggers completion, but is canceled before
pm_wakeup_pending(), so need reinit to restart the
wait_for_completion() process.
2. Handling back-to-back suspend attempts: after a subsequent suspend
attempt finishes waiting for a previous suspend's fs_sync to finish,
we need the reinit to start the wait_for_completion() process of the
subsequent suspend's fs_sync.

> > +             /*
> > +              * Handle the case where a sleep immediately follows a previous
> > +              * sleep that was aborted during fs_sync. In this case, wait for
> > +              * the previous filesystem sync to finish. Then do another
> > +              * filesystem sync so any subsequent filesystem changes are
> > +              * synced before sleeping.
> > +              */
> > +             if (pm_sleep_fs_sync_queued) {
> > +                     need_pm_sleep_fs_sync_requeue = true;
> > +             } else {
> > +                     need_pm_sleep_fs_sync_requeue = false;
> > +                     pm_sleep_fs_sync_queued = true;
> > +                     schedule_work(&sync_filesystems);
> > +             }
> > +             spin_unlock_irqrestore(&pm_sleep_fs_sync_lock, flags);
> > +
> > +             /*
> > +              * Completion is triggered by fs_sync finishing or an abort sleep
> > +              * signal, whichever comes first
> > +              */
> > +             wait_for_completion(&pm_sleep_fs_sync_complete);
> > +             if (pm_wakeup_pending())
> > +                     return -EBUSY;
> > +     } while (need_pm_sleep_fs_sync_requeue);
> > +
> > +     return 0;
> > +}
> > +