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

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Message-Id: <200703090811.38559.rjw@sisk.pl>
Date:	Fri, 9 Mar 2007 08:11:37 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Len Brown <lenb@...nel.org>
Cc:	shaohua.li@...el.com, Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	Dave Jones <davej@...hat.com>
Subject: Re: [PATCH] swsusp: Disable nonboot CPUs before entering platform suspend

On Friday, 9 March 2007 02:11, Len Brown wrote:
> On Wednesday 07 March 2007 18:13, Rafael J. Wysocki wrote:
> > 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.
> > 
> 
> Shaohua added it between 2.6.17 and 2.6.18
> 55b2355eefc2f160246226d4d69fed431173a4d5

Yes, DaveJ has already noticed that, but what it's there for?

Rafael
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