Re: [PATCH v2 1/3] PM suspend/hibernate: Call notifier after freezing processes

From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: "Pali Rohár" <pali.rohar@gmail.com>
Cc: Alasdair Kergon <agk@redhat.com>,
	Mike Snitzer <snitzer@redhat.com>, Neil Brown <neilb@suse.de>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	dm-devel@redhat.com, linux-raid@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v2 1/3] PM suspend/hibernate: Call notifier after freezing processes
Date: Sat, 18 Jul 2015 01:27:15 +0200	[thread overview]
Message-ID: <3179448.TScsKEAuyR@vostro.rjw.lan> (raw)
In-Reply-To: <20150716073302.GA10393@pali>

On Thursday, July 16, 2015 09:33:02 AM Pali Rohár wrote:
> On Thursday 16 July 2015 03:02:03 Rafael J. Wysocki wrote:
> > On Sunday, June 21, 2015 01:20:32 PM Pali Rohár wrote:
> > > To prevent race conditions on userspace processes with I/O some taks must be
> > > called after processes are freezed. This patch adds new events which are
> > > delivered by pm_notifier_call_chain() after freezing processes when doing
> > > suspend or hibernate action.
> > > 
> > > Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
> > > ---
> > >  include/linux/suspend.h  |    2 ++
> > >  kernel/power/hibernate.c |    2 ++
> > >  kernel/power/suspend.c   |    4 +++-
> > >  3 files changed, 7 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/include/linux/suspend.h b/include/linux/suspend.h
> > > index 5efe743..bc743c8 100644
> > > --- a/include/linux/suspend.h
> > > +++ b/include/linux/suspend.h
> > > @@ -368,6 +368,8 @@ static inline bool hibernation_available(void) { return false; }
> > >  #define PM_POST_SUSPEND		0x0004 /* Suspend finished */
> > >  #define PM_RESTORE_PREPARE	0x0005 /* Going to restore a saved image */
> > >  #define PM_POST_RESTORE		0x0006 /* Restore failed */
> > > +#define PM_HIBERNATION_AFTER_FREEZE	0x0007 /* After hibernation freeze */
> > > +#define PM_SUSPEND_AFTER_FREEZE		0x0008 /* After suspend freeze */
> > >  
> > >  extern struct mutex pm_mutex;
> > >  
> > > diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> > > index 2329daa..184f7ee 100644
> > > --- a/kernel/power/hibernate.c
> > > +++ b/kernel/power/hibernate.c
> > > @@ -671,6 +671,8 @@ int hibernate(void)
> > >  	if (error)
> > >  		goto Exit;
> > >  
> > > +	pm_notifier_call_chain(PM_HIBERNATION_AFTER_FREEZE);
> > 
> > Don't we need to check errors from these?
> > 
> 
> If yes, what to do in this case? Fail hibernation and goto Exit?

Yes, fail the transition in progress.

> > Also, if you're adding AFTER_FREEZE, it would be good to add BEFORE_THAW too
> > for symmetry.
> > 
> 
> But there is no use case for BEFORE_THAW. At least it is not needed for now.

For your use case, a single function pointer would be sufficient too.

> > > +
> > >  	lock_device_hotplug();
> > >  	/* Allocate memory management structures */
> > >  	error = create_basic_memory_bitmaps();
> > > diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> > > index 8d7a1ef..ba2a945 100644
> > > --- a/kernel/power/suspend.c
> > > +++ b/kernel/power/suspend.c
> > > @@ -277,8 +277,10 @@ static int suspend_prepare(suspend_state_t state)
> > >  	trace_suspend_resume(TPS("freeze_processes"), 0, true);
> > >  	error = suspend_freeze_processes();
> > >  	trace_suspend_resume(TPS("freeze_processes"), 0, false);
> > > -	if (!error)
> > > +	if (!error) {
> > > +		pm_notifier_call_chain(PM_SUSPEND_AFTER_FREEZE);
> > >  		return 0;
> > > +	}
> > >  
> > >  	suspend_stats.failed_freeze++;
> > >  	dpm_save_failed_step(SUSPEND_FREEZE);
> > > 
> > 
> 
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.