Re: [RFC][PATCH] PM / Sleep: Freeze filesystems during system suspend/hibernation

[Rafael J. Wysocki]

On Sunday, January 29, 2012, Srivatsa S. Bhat wrote:
> On 01/28/2012 07:15 PM, Rafael J. Wysocki wrote:
> 
> > From: Rafael J. Wysocki <rjw@xxxxxxx>
> > 
> > Freeze all filesystems during system suspend and (kernel-driven)
> > hibernation by calling freeze_supers() for all superblocks and thaw
> > them during the subsequent resume with the help of thaw_supers().
> > 
> > This makes filesystems stay in a consistent state in case something
> > goes wrong between system suspend (or hibernation) and the subsequent
> > resume (e.g. journal replays won't be necessary in those cases).  In
> > particular, this should help to solve a long-standing issue that, in
> > some cases, during resume from hibernation the boot loader causes the
> > journal to be replied for the filesystem containing the kernel image
> 
> > and/or initrd causing it to become inconsistent with the information
> 
> > stored in the hibernation image.
> > 
> > The user-space-driven hibernation (s2disk) is not covered by this
> > change, because the freezing of filesystems prevents s2disk from
> > accessing device special files it needs to do its job.
> > 
> > This change is based on earlier work by Nigel Cunningham.
> > 
> > Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
> > ---
> >  fs/super.c               |   73 +++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/fs.h       |    3 +
> >  kernel/power/hibernate.c |   11 +++++--
> >  kernel/power/power.h     |   23 --------------
> >  kernel/power/suspend.c   |   42 +++++++++++++++++++++++++++
> >  5 files changed, 128 insertions(+), 24 deletions(-)
> > 
> 
> ...
> 
> > Index: linux/kernel/power/suspend.c
> > ===================================================================
> > --- linux.orig/kernel/power/suspend.c
> > +++ linux/kernel/power/suspend.c
> > @@ -29,6 +29,48 @@
> > 
> >  #include "power.h"
> > 
> > +#ifdef CONFIG_SUSPEND_FREEZER
> > +
> > +static inline int suspend_freeze_processes(void)
> > +{
> > +	int error;
> > +
> > +	error = freeze_processes();
> > +	if (error)
> > +		return error;
> > +
> > +	error = freeze_supers();
> > +	if (error) {
> > +		thaw_processes();
> > +		return error;
> > +	}
> > +
> > +	error = freeze_kernel_threads();
> > +	if (error)
> > +		thaw_supers();
> > +
> 
> 
> If freezing of kernel threads fails, freeze_kernel_threads() calls
> thaw_processes(), which means, even userspace processes get thawed.
> So, there would be a time-window in which userspace is thawed but the
> filesystems are still frozen. That is not very desirable right?

No, it is not.  I overlooked that, thanks!

> If that is right, then modifying freeze_kernel_threads() to call
> thaw_kernel_threads() instead of thaw_processes() would fix it
> (and of course, we would need to explicitly call thaw_processes
> above).
> 
> BTW, after your patch posted at https://lkml.org/lkml/2012/1/27/501,
> I very much wanted to write a patch to convert the semantics of
> freeze/thaw to something like:
> 
> freeze_processes() calls thaw_processes on error.
> //Both touch only userspace processes.
> 
> freeze_kernel_threads() calls thaw_kernel_threads() on error.
> //Both touch only kernel threads.
> 
> Of course, such a patch would need to do a lot of fixing up at several
> places, but IMHO, it would really help make the overall code more logical
> and easier to understand.
> 
> I can write it up and post it soon, but then you'll have to rebase
> your patch (this one) on top of that. What do you say?

Please do that, it wouldn't be any problem for me to rebase the $subject
patch.

Thanks,
Rafael


> > +	return error;
> > +}
> > +
> > +static inline void suspend_thaw_processes(void)
> > +{
> > +	thaw_supers();
> > +	thaw_processes();
> > +}
> > +
> > +#else /* !CONFIG_SUSPEND_FREEZER */
> > +
> > +static inline int suspend_freeze_processes(void)
> > +{
> > +	return 0;
> > +}
> > +
> > +static inline void suspend_thaw_processes(void)
> > +{
> > +}
> > +
> > +#endif /* !CONFIG_SUSPEND_FREEZER */
> > +
> >  const char *const pm_states[PM_SUSPEND_MAX] = {
> >  	[PM_SUSPEND_STANDBY]	= "standby",
> >  	[PM_SUSPEND_MEM]	= "mem",
> > Index: linux/kernel/power/hibernate.c
> > ===================================================================
> > --- linux.orig/kernel/power/hibernate.c
> > +++ linux/kernel/power/hibernate.c
> > @@ -626,12 +626,17 @@ int hibernate(void)
> >  	if (error)
> >  		goto Finish;
> > 
> > -	error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
> > +	error = freeze_supers();
> >  	if (error)
> >  		goto Thaw;
> > +
> > +	error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
> > +	if (error)
> > +		goto Thaw_fs;
> > +
> >  	if (freezer_test_done) {
> >  		freezer_test_done = false;
> > -		goto Thaw;
> > +		goto Thaw_fs;
> >  	}
> > 
> >  	if (in_suspend) {
> > @@ -655,6 +660,8 @@ int hibernate(void)
> >  		pr_debug("PM: Image restored successfully.\n");
> >  	}
> > 
> > + Thaw_fs:
> > +	thaw_supers();
> >   Thaw:
> >  	thaw_processes();
> >   Finish:
> > 
> 
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