linux-kernel - Re: [PATCH v2] PM / Sleep: fix recovery during s2ram/hibernation

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Date:	Fri, 24 Oct 2014 17:17:12 +0300
From:	Imre Deak <imre.deak@...el.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Pavel Machek <pavel@....cz>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PM / Sleep: fix recovery during s2ram/hibernation

On Fri, 2014-10-24 at 16:04 +0200, Rafael J. Wysocki wrote:
> On Friday, October 24, 2014 10:59:09 AM Imre Deak wrote:
> > Atm, if one of the dev_pm_ops::freeze callbacks fails during the QUIESCE
> > phase we don't rollback things correctly calling the thaw and complete
> > callbacks. This could leave some devices in a suspended state in case of
> > an error during resuming from hibernation.
> > 
> > Also if an asynchronous suspend_late or freeze_late callback fails
> > during the SUSPEND, FREEZE or QUIESCE phases we don't propagate the
> > corresponding error correctly, in effect ignoring the error and
> > continuing the suspend-to-ram/hibernation. During suspend-to-ram this
> > could leave some devices without a valid saved context, leading to a
> > failure to reinitialize them during resume. During hibernation this
> > could leave some devices active interfeering with the creation /
> > restoration of the hibernation image. Also this could leave the
> > corresponding devices without a valid saved context and failure to
> > reinitialize them during resume.
> > 
> > v2:
> > - call dpm_resume_end() unconditionally, it's guaranteed that error
> >   is non-zero
> > 
> > Signed-off-by: Imre Deak <imre.deak@...el.com>
> 
> These are two unrelated fixes, so please send them as two patches.
> 
> > ---
> >  drivers/base/power/main.c | 2 ++
> >  kernel/power/hibernate.c  | 3 ++-
> >  2 files changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > index 4497319..9717d5f 100644
> > --- a/drivers/base/power/main.c
> > +++ b/drivers/base/power/main.c
> > @@ -1266,6 +1266,8 @@ int dpm_suspend_late(pm_message_t state)
> >  	}
> >  	mutex_unlock(&dpm_list_mtx);
> >  	async_synchronize_full();
> > +	if (!error)
> > +		error = async_error;
> >  	if (error) {
> >  		suspend_stats.failed_suspend_late++;
> >  		dpm_save_failed_step(SUSPEND_SUSPEND_LATE);
> 
> So the above will be the first fix and the below will be the second one.

Ok.

> 
> > diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> > index a9dfa79..594ee7f 100644
> > --- a/kernel/power/hibernate.c
> > +++ b/kernel/power/hibernate.c
> > @@ -502,8 +502,9 @@ int hibernation_restore(int platform_mode)
> >  	error = dpm_suspend_start(PMSG_QUIESCE);
> >  	if (!error) {
> >  		error = resume_target_kernel(platform_mode);
> > -		dpm_resume_end(PMSG_RECOVER);
> > +		BUG_ON(!error);
> 
> Why BUG_ON()?  Is crashing the kernel necessary here?

I figured that this being an undefined state after restoration of a
memory image, it's better to crash than to continue and risk corrupting
some user data.

> 
> >  	}
> > +	dpm_resume_end(PMSG_RECOVER);
> >  	pm_restore_gfp_mask();
> >  	resume_console();
> >  	pm_restore_console();
> > 
> 


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