On Tue, Oct 24, 2023 at 10:31 AM +08, Xuan Zhuo wrote:
> On Mon, 23 Oct 2023 18:52:45 +0200, Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> wrote:
>> On Thu, Oct 19, 2023 at 08:55 PM +08, Xuan Zhuo wrote:
>> > On Thu, 19 Oct 2023 12:16:24 +0200, Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> wrote:
>> >> Since commit 19e226e8cc5d ("virtio: Make vp_set_vq_affinity() take a
>> >> mask.") it is actually not needed to have a local copy of the cpu mask.
>> >
>> >
>> > Could you give more info to prove this?
>
>
> Actually, my question is that can we pass a val on the stack(or temp value) to
> the irq_set_affinity_hint()?
>
> Such as the virtio-net uses zalloc_cpumask_var to alloc a cpu_mask, and
> that will be released.
>
>
>
> int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,
> bool setaffinity)
> {
> unsigned long flags;
> struct irq_desc *desc = irq_get_desc_lock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
>
> if (!desc)
> return -EINVAL;
> -> desc->affinity_hint = m;
> irq_put_desc_unlock(desc, flags);
> if (m && setaffinity)
> __irq_set_affinity(irq, m, false);
> return 0;
> }
> EXPORT_SYMBOL_GPL(__irq_apply_affinity_hint);
>
> The above code directly refers the mask pointer. If the mask is a temp value, I
> think that is a bug.
You are completely right. irq_set_affinity_hint stores the mask pointer.
irq_affinity_hint_proc_show later dereferences it when user reads out
/proc/irq/*/affinity_hint.
I have failed to notice that. That's why we need cpumask_copy to stay.
My patch is buggy. Please disregard.
I will send a v2 to only migrate from deprecated irq_set_affinity_hint.
> And I notice that many places directly pass the temp value to this API.
> And I am a little confused. ^_^ Or I missed something.
There seem two be two gropus of callers:
1. Those that use get_cpu_mask/cpumask_of/cpumask_of_node to produce a
cpumask pointer which is a preallocated constant.
$ weggli 'irq_set_affinity_hint(_, $func(_));' ~/src/linux
2. Those that pass a pointer to memory somewhere.
$ weggli 'irq_set_affinity_hint(_, $mask);' ~/src/linux
(weggli tool can be found at https://github.com/weggli-rs/weggli)
I've looked over the callers from group #2 but I couldn't find any
passing a pointer memory on stack :-)
Thanks for pointing this out.
[...]
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