linux-kernel - Re: [PATCH] apic: use GFP_ATOMIC in lapic

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Date:	Tue, 28 Dec 2010 15:56:23 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] apic: use GFP_ATOMIC in lapic_resume

On Tue, 2010-12-28 at 15:39 +0800, David Rientjes wrote:
> On Tue, 28 Dec 2010, Zhang Rui wrote:
> 
> > > > Index: linux-2.6/arch/x86/kernel/apic/apic.c
> > > > ===================================================================
> > > > --- linux-2.6.orig/arch/x86/kernel/apic/apic.c
> > > > +++ linux-2.6/arch/x86/kernel/apic/apic.c
> > > > @@ -1459,7 +1459,7 @@ void __init enable_IR_x2apic(void)
> > > >  	if (dmar_table_init_ret && !x2apic_supported())
> > > >  		return;
> > > >  
> > > > -	ioapic_entries = alloc_ioapic_entries();
> > > > +	ioapic_entries = alloc_ioapic_entries(GFP_KERNEL);
> > > >  	if (!ioapic_entries) {
> > > >  		pr_err("Allocate ioapic_entries failed\n");
> > > >  		goto out;
> > > > @@ -2084,7 +2084,7 @@ static int lapic_resume(struct sys_devic
> > > >  
> > > >  	local_irq_save(flags);
> > > >  	if (intr_remapping_enabled) {
> > > > -		ioapic_entries = alloc_ioapic_entries();
> > > > +		ioapic_entries = alloc_ioapic_entries(GFP_ATOMIC);
> > > >  		if (!ioapic_entries) {
> > > >  			WARN(1, "Alloc ioapic_entries in lapic resume failed.");
> > > >  			ret = -ENOMEM;
> > > 
> > > You can't do the allocation before disabling irqs when 
> > > intr_remapping_enabled is set?
> > 
> > yes, we can. The first idea came into my mind is to register a pm
> > notifier callback to allocate/free the memory. But that one duplicates
> > the code of alloc_ioapic_entries, which doesn't look nice, neither.
> > Plus, is there any problem with this one?
> > 
> 
> We try to avoid GFP_ATOMIC whenever possible and this seems like a 
> particularly trivial case.  You can simply move the alloc_ioapic_entries() 
> and NULL check before local_irq_save() and GFP_KERNEL will work fine.

I'm afraid not.
lapic_resume is invoked in sysdev_resume, which is done with irq
disabled, please refer to the code in kernel/power/suspend.c.

        arch_suspend_disable_irqs();
        BUG_ON(!irqs_disabled()); 

        error = sysdev_suspend(PMSG_SUSPEND);
        if (!error) {    
                if (!suspend_test(TEST_CORE) &&
pm_check_wakeup_events()) {
                        error = suspend_ops->enter(state);
                        events_check_enabled = false;
                }
                sysdev_resume();
        }       
        
        arch_suspend_enable_irqs();
        BUG_ON(irqs_disabled());

To pre-allocate the memory, we need to build a notifier bloack and call
register_pm_notifier.

thanks,
rui
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