linux-kernel - Re: [PATCH] swsusp: Disable nonboot CPUs before entering platform suspend

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Message-Id: <200703080013.05544.rjw@sisk.pl>
Date:	Thu, 8 Mar 2007 00:13:05 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH] swsusp: Disable nonboot CPUs before entering platform suspend

On Wednesday, 7 March 2007 23:49, Andrew Morton wrote:
> On Wed, 7 Mar 2007 23:14:29 +0100
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > On Wednesday, 7 March 2007 22:16, Andrew Morton wrote:
> > > On Wed, 7 Mar 2007 20:44:11 +0100
> > > "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> > > 
> > > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > > 
> > > > Prevent the WARN_ON() in arch/x86_64/kernel/acpi/sleep.c:init_low_mapping()
> > > > from triggering by disabling nonboot CPUs before we finally enter the platform
> > > > suspend.
> > > > 
> > > > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > > > ---
> > > >  kernel/power/disk.c |    1 +
> > > >  kernel/power/user.c |    2 +-
> > > >  2 files changed, 2 insertions(+), 1 deletion(-)
> > > > 
> > > > Index: linux-2.6.21-rc2-mm2/kernel/power/disk.c
> > > > ===================================================================
> > > > --- linux-2.6.21-rc2-mm2.orig/kernel/power/disk.c
> > > > +++ linux-2.6.21-rc2-mm2/kernel/power/disk.c
> > > > @@ -61,6 +61,7 @@ static void power_down(suspend_disk_meth
> > > >  	switch(mode) {
> > > >  	case PM_DISK_PLATFORM:
> > > >  		if (pm_ops && pm_ops->enter) {
> > > > +			disable_nonboot_cpus();
> > > >  			kernel_shutdown_prepare(SYSTEM_SUSPEND_DISK);
> > > >  			pm_ops->enter(PM_SUSPEND_DISK);
> > > >  			break;
> > > > Index: linux-2.6.21-rc2-mm2/kernel/power/user.c
> > > > ===================================================================
> > > > --- linux-2.6.21-rc2-mm2.orig/kernel/power/user.c
> > > > +++ linux-2.6.21-rc2-mm2/kernel/power/user.c
> > > > @@ -398,9 +398,9 @@ static int snapshot_ioctl(struct inode *
> > > >  
> > > >  		case PMOPS_ENTER:
> > > >  			if (data->platform_suspend) {
> > > > +				disable_nonboot_cpus();
> > > >  				kernel_shutdown_prepare(SYSTEM_SUSPEND_DISK);
> > > >  				error = pm_ops->enter(PM_SUSPEND_DISK);
> > > > -				error = 0;
> > > >  			}
> > > >  			break;
> > > 
> > > Is this considered 2.6.21 material?  If so why?
> > 
> > Well, the WARN_ON() in arch/x86_64/kernel/acpi/sleep.c:init_low_mapping()
> > triggers every time an SMP x86_64 box is suspended to disk using the platform
> > mode (default), which is quite annoying IMHO and users think something wrong is
> > going on.  This will probably cause them to report the problem and I'd rather
> > like to avoid handling these reports. ;-)
> 
> Well sure - if patches were always error-free, we'd always apply them
> immediately.
> 
> The question is: is the risk of this patch breaking things exceeded by the
> benefit which you describe?

Well, it has survived some testing (http://lkml.org/lkml/2007/3/7/16).  Also,
before the code ordering in 2.6.21-rc* we had been running on one CPU
here, so I think the risk is small.

We could remove the WARN_ON() as Pavel has just suggested, but first I'd like
to know who put it there and why.

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