On Tuesday, November 30, 2010, Hugh Dickins wrote:
quoted text
> On Sat, 27 Nov 2010, Rafael J. Wysocki wrote:
> > On Saturday, November 27, 2010, Ondrej Zary wrote:
> > > > > >
> > > > > > Not signing it off yet,
> > > > > > Hugh
> > > > >
> > > > > Could you please do that? The patch fixes the problem.
> 
> Sorry for going quiet for so long.
> 
> Thanks for testing, Ondrej.  I completely agree with Rafael that my
> patch was inadequate: it turned out to be good enough for your useful
> feedback on the main path through hibernation, but missed a number
> of details.  We do need something like Rafael's patch - thanks.
> 
> (And I realize that it's tiresome and frustrating for you to be
> trying first that and then this etc; but we had bugs here precisely
> because this is a confusing area, so I think it is worth some effort
> to get right now.)
> 
> > > >
> > > > Can you check if the problem is also fixed by the patch below, please?
> > > 
> > > The patch does not apply to 2.6.35.4, 2.6.35.5 and also 2.6.36. What version 
> > > should I test?
> > 
> > The patch was against the current mainline.
> > 
> > The one below was rebased on top of 2.6.36, so please test it with this kernel.
> 
> I'll comment on this version, since it has one more line than your original.
> 
> > 
> > Thanks,
> > Rafael
> > 
> > ---
> >  kernel/power/hibernate.c |   36 ++++++++++++++++++++++++++----------
> >  kernel/power/power.h     |    1 +
> >  kernel/power/user.c      |    2 ++
> >  3 files changed, 29 insertions(+), 10 deletions(-)
> > 
> > Index: suspend-2.6/kernel/power/hibernate.c
> > ===================================================================
> > --- suspend-2.6.orig/kernel/power/hibernate.c
> > +++ suspend-2.6/kernel/power/hibernate.c
> > @@ -29,6 +29,21 @@
> >  #include "power.h"
> >  
> >  
> > +static gfp_t saved_gfp_mask;
> > +
> > +static void hibernate_restrict_gfp_mask(void)
> > +{
> > +	saved_gfp_mask = clear_gfp_allowed_mask(GFP_IOFS);
> > +}
> > +
> > +void hibernate_restore_gfp_mask(void)
> > +{
> > +	if (saved_gfp_mask) {
> > +		set_gfp_allowed_mask(saved_gfp_mask);
> > +		saved_gfp_mask = 0;
> > +	}
> > +}
> > +
> 
> Trivial point, I suppose, but it bothers me that PM is accumulating
> wrappers around wrappers around gfp_allowed_mask.  Looks like
> clear_gfp_allowed_mask and set_gfp_allowed_mask (oddly asymmetrical)
> were not really what we need.  How about scrapping them, and putting
> pm_restrict_gfp_mask() and pm_restore_gfp_mask() into page_alloc.c?

Sure, that sounds like a good idea indeed.

quoted text
> >  static int noresume = 0;
> >  static char resume_file[256] = CONFIG_PM_STD_PARTITION;
> >  dev_t swsusp_resume_device;
> > @@ -326,7 +341,6 @@ static int create_image(int platform_mod
> >  int hibernation_snapshot(int platform_mode)
> >  {
> >  	int error;
> > -	gfp_t saved_mask;
> >  
> >  	error = platform_begin(platform_mode);
> >  	if (error)
> > @@ -338,7 +352,7 @@ int hibernation_snapshot(int platform_mo
> >  		goto Close;
> >  
> >  	suspend_console();
> > -	saved_mask = clear_gfp_allowed_mask(GFP_IOFS);
> > +	hibernate_restrict_gfp_mask();
> 
> Yes.
> 
> >  	error = dpm_suspend_start(PMSG_FREEZE);
> >  	if (error)
> >  		goto Recover_platform;
> > @@ -347,7 +361,10 @@ int hibernation_snapshot(int platform_mo
> >  		goto Recover_platform;
> >  
> >  	error = create_image(platform_mode);
> > -	/* Control returns here after successful restore */
> > +	/*
> > +	 * Control returns here (1) after the image has been created or the
> > +	 * image creation has failed and (2) after a successful restore.
> > +	 */
> >  
> >   Resume_devices:
> >  	/* We may need to release the preallocated image pages here. */
> > @@ -356,7 +373,10 @@ int hibernation_snapshot(int platform_mo
> >  
> >  	dpm_resume_end(in_suspend ?
> >  		(error ? PMSG_RECOVER : PMSG_THAW) : PMSG_RESTORE);
> > -	set_gfp_allowed_mask(saved_mask);
> > +
> > +	if (error || !in_suspend)
> > +		hibernate_restore_gfp_mask();
> > +
> 
> I'm worried that it's hard to find and maintain the places that need
> this restoration - and if we miss one, we won't find out about it for
> ages.  It would help a lot if the gfp restoration always accompanies
> some other essential stage - thaw_processes() looks to be right,
> so could we skip conditionally restoring here if we do it then?
> 
> I suggest that in part because I cannot find where you restore in
> the case that hibernate()'s swsusp_write() fails - that was the
> case that made me realize my little patch was too simplistic.

Good point.  I'm not totally sure if coupling this with thaw_processes() is
the right thing yet, but I guess it is, except for the s2disk-specific things
below.

quoted text
> >  	resume_console();
> >   Close:
> >  	platform_end(platform_mode);
> > @@ -451,17 +471,16 @@ static int resume_target_kernel(bool pla
> >  int hibernation_restore(int platform_mode)
> >  {
> >  	int error;
> > -	gfp_t saved_mask;
> >  
> >  	pm_prepare_console();
> >  	suspend_console();
> > -	saved_mask = clear_gfp_allowed_mask(GFP_IOFS);
> > +	hibernate_restrict_gfp_mask();
> 
> Yes.
> 
> >  	error = dpm_suspend_start(PMSG_QUIESCE);
> >  	if (!error) {
> >  		error = resume_target_kernel(platform_mode);
> >  		dpm_resume_end(PMSG_RECOVER);
> >  	}
> > -	set_gfp_allowed_mask(saved_mask);
> > +	hibernate_restore_gfp_mask();
> 
> But this could be left until software_resume()'s thaw_processes()?
> Ah, that won't cover the SNAPSHOT_ATOMIC_RESTORE case, hmmm.

That's correct.

quoted text
> >  	resume_console();
> >  	pm_restore_console();
> >  	return error;
> > @@ -475,7 +494,6 @@ int hibernation_restore(int platform_mod
> >  int hibernation_platform_enter(void)
> >  {
> >  	int error;
> > -	gfp_t saved_mask;
> >  
> >  	if (!hibernation_ops)
> >  		return -ENOSYS;
> > @@ -491,7 +509,6 @@ int hibernation_platform_enter(void)
> >  
> >  	entering_platform_hibernation = true;
> >  	suspend_console();
> > -	saved_mask = clear_gfp_allowed_mask(GFP_IOFS);
> 
> Right.
> 
> >  	error = dpm_suspend_start(PMSG_HIBERNATE);
> >  	if (error) {
> >  		if (hibernation_ops->recover)
> > @@ -535,7 +552,6 @@ int hibernation_platform_enter(void)
> >   Resume_devices:
> >  	entering_platform_hibernation = false;
> >  	dpm_resume_end(PMSG_RESTORE);
> > -	set_gfp_allowed_mask(saved_mask);
> 
> Right.
> 
> >  	resume_console();
> >  
> >   Close:
> > Index: suspend-2.6/kernel/power/power.h
> > ===================================================================
> > --- suspend-2.6.orig/kernel/power/power.h
> > +++ suspend-2.6/kernel/power/power.h
> > @@ -49,6 +49,7 @@ static inline char *check_image_kernel(s
> >  extern int hibernation_snapshot(int platform_mode);
> >  extern int hibernation_restore(int platform_mode);
> >  extern int hibernation_platform_enter(void);
> > +extern void hibernate_restore_gfp_mask(void);
> >  #endif
> >  
> >  extern int pfn_is_nosave(unsigned long);
> > Index: suspend-2.6/kernel/power/user.c
> > ===================================================================
> > --- suspend-2.6.orig/kernel/power/user.c
> > +++ suspend-2.6/kernel/power/user.c
> > @@ -263,6 +263,7 @@ static long snapshot_ioctl(struct file *
> >  	case SNAPSHOT_UNFREEZE:
> >  		if (!data->frozen || data->ready)
> >  			break;
> > +		hibernate_restore_gfp_mask();
> 
> Right, here you have one next to thaw_processes().
> But the SNAPSHOT ioctls are a nightmarish maze to me,
> I cannot comment much on what's right here.

Well, sorry about that.  A few of them should just be dropped, but they are
lingering so that oldish user space works with the new kernels.

Perhaps it's time to just drop them ...

quoted text
> >  		thaw_processes();
> >  		usermodehelper_enable();
> >  		data->frozen = 0;
> > @@ -275,6 +276,7 @@ static long snapshot_ioctl(struct file *
> >  			error = -EPERM;
> >  			break;
> >  		}
> > +		hibernate_restore_gfp_mask();
> >  		error = hibernation_snapshot(data->platform_support);
> 
> That might be good safety, but it does strongly suggest that you
> needed to put it somewhere else, and couldn't work out where?

This is because of how s2disk works.  If it fails to allocate enough swap,
it tries again with minimum image size without thawing the other tasks.
Now, because hibernation_snapshot() saves the "original" GFP mask, it has
to be restored before calling that function.

quoted text
> >  		if (!error)
> >  			error = put_user(in_suspend, (int __user *)arg);
> > 

Thanks,
Rafael
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