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

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Message-ID: <52E55FB1.4060404@redhat.com>
Date:	Sun, 26 Jan 2014 14:19:13 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Yinghai Lu <yinghai@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	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



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?

P.
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