linux-kernel - Re: [PATCH -v2] x86: allocate cpumask during check irq vectors

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Date:	Sun, 26 Jan 2014 12:23:13 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>, Prarit Bhargava <prarit@...hat.com>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v2] x86: allocate cpumask during check irq vectors

s/global/static/, with a big loud comment why it is okay.

Ingo Molnar <mingo@...nel.org> wrote:
>
>* Prarit Bhargava <prarit@...hat.com> wrote:
>
>> 
>> 
>> On 01/26/2014 08:32 AM, Ingo Molnar wrote:
>> > 
>> > * Prarit Bhargava <prarit@...hat.com> wrote:
>> > 
>> >> On 01/25/2014 03:02 AM, Ingo Molnar wrote:
>> >>>
>> >>> * Yinghai Lu <yinghai@...nel.org> wrote:
>> >>>
>> >>>> Fix warning:
>> >>>> arch/x86/kernel/irq.c: In function
>check_irq_vectors_for_cpu_disable:
>> >>>> arch/x86/kernel/irq.c:337:1: warning: the frame size of 2052
>bytes is larger than 2048 bytes
>> >>>>
>> >>>> when NR_CPUS=8192
>> >>>>
>> >>>> We should use zalloc_cpumask_var() instead.
>> >>>>
>> >>>> -v2: update to GFP_ATOMIC instead and free the allocated cpumask
>at last.
>> >>>>
>> >>>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>> >>>> Cc: Prarit Bhargava <prarit@...hat.com>
>> >>>>
>> >>>> ---
>> >>>>  arch/x86/kernel/irq.c |   24 +++++++++++++++++-------
>> >>>>  1 file changed, 17 insertions(+), 7 deletions(-)
>> >>>>
>> >>>> Index: linux-2.6/arch/x86/kernel/irq.c
>> >>>>
>===================================================================
>> >>>> --- linux-2.6.orig/arch/x86/kernel/irq.c
>> >>>> +++ linux-2.6/arch/x86/kernel/irq.c
>> >>>> @@ -277,11 +277,18 @@ int check_irq_vectors_for_cpu_disable(vo
>> >>>>  	unsigned int this_cpu, vector, this_count, count;
>> >>>>  	struct irq_desc *desc;
>> >>>>  	struct irq_data *data;
>> >>>> -	struct cpumask affinity_new, online_new;
>> >>>> +	cpumask_var_t affinity_new, online_new;
>> >>>> +
>> >>>> +	if (!alloc_cpumask_var(&affinity_new, GFP_ATOMIC))
>> >>>> +		return -ENOMEM;
>> >>>> +	if (!alloc_cpumask_var(&online_new, GFP_ATOMIC)) {
>> >>>> +		free_cpumask_var(affinity_new);
>> >>>> +		return -ENOMEM;
>> >>>> +	}
>> >>>
>> >>> Atomic allocations can fail easily if the system is under duress.
>> >>
>> >> Then the hotplug attempt will fail which IMO is okay. [...]
>> > 
>> > Which is not OK at all for reliable operation, if the system has 
>> > otherwise gobs of RAM, which just don't happen to be atomic 
>> > allocatable!
>> 
>> Ingo, I'm really not sure what other option there is here.  Care to 
>> suggest one?
>
>Since only ever a single instance of this code will run, can it simply 
>be a global cpumask_t variable?
>
>Thanks,
>
>	Ingo

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.
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