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 17:16:59 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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


* 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.

Thanks,

	Ingo