linux-kernel - Re: [PATCH] kernel: x86: apic: Replace GFP_ATOMIC with GFP_KERNEL in __add_pin_to_irq

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Date:   Tue, 13 Feb 2018 17:20:18 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ingo Molnar <mingo@...nel.org>
cc:     Jia-Ju Bai <baijiaju1990@...il.com>, mingo@...hat.com,
        hpa@...or.com, jgross@...e.com, douly.fnst@...fujitsu.com,
        kkamagui@...il.com, gregkh@...uxfoundation.org, mka@...omium.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] kernel: x86: apic: Replace GFP_ATOMIC with GFP_KERNEL
 in __add_pin_to_irq_node

On Tue, 13 Feb 2018, Ingo Molnar wrote:
> * Thomas Gleixner <tglx@...utronix.de> wrote:
> > On Tue, 13 Feb 2018, Ingo Molnar wrote:
> > > * Jia-Ju Bai <baijiaju1990@...il.com> wrote:
> > > 
> > > > The function __add_pin_to_irq_node is not called in atomic context.
> > > > Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
> > > > 
> > > > Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> > > > ---
> > > >  arch/x86/kernel/apic/io_apic.c |    2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> > > > index 201579d..665c013 100644
> > > > --- a/arch/x86/kernel/apic/io_apic.c
> > > > +++ b/arch/x86/kernel/apic/io_apic.c
> > > > @@ -379,7 +379,7 @@ static int __add_pin_to_irq_node(struct mp_chip_data *data,
> > > >  		if (entry->apic == apic && entry->pin == pin)
> > > >  			return 0;
> > > >  
> > > > -	entry = kzalloc_node(sizeof(struct irq_pin_list), GFP_ATOMIC, node);
> > > > +	entry = kzalloc_node(sizeof(struct irq_pin_list), GFP_KERNEL, node);
> > > >  	if (!entry) {
> > > >  		pr_err("can not alloc irq_pin_list (%d,%d,%d)\n",
> > > >  		       node, apic, pin);
> > > 
> > > NAK: this is called in an atomic section: with IRQs disabled ...
> > 
> > The only invocation where this happens with IRQs disabled is the early
> > check_timer() code which runs _before_ the scheduler is working. GFP_KERNEL
> > is valid during that phase. All other call sites have interrupts enabled.
> 
> Yeah, so at minimum there's a mismatch between the changelog:
> 
> > > > The function __add_pin_to_irq_node is not called in atomic context.
> 
> ... and actual behavior. What you wrote should be part of the changelog I suspect.

Fair enough.