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

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Message-ID: <alpine.DEB.2.00.1012272336001.25826@chino.kir.corp.google.com>
Date:	Mon, 27 Dec 2010 23:39:28 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Zhang Rui <rui.zhang@...el.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, 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.
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