Jakub Sitnicki
2023-Oct-24 08:17 UTC
[PATCH 1/2] virtio_pci: Don't make an extra copy of cpu affinity mask
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 at cloudflare.com> 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 at cloudflare.com> 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. [...]
Xuan Zhuo
2023-Oct-24 10:53 UTC
[PATCH 1/2] virtio_pci: Don't make an extra copy of cpu affinity mask
On Tue, 24 Oct 2023 10:17:19 +0200, Jakub Sitnicki <jakub at cloudflare.com> wrote:> 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 at cloudflare.com> 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 at cloudflare.com> 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 :-)Pls check stmmac_request_irq_multi_msi() Thanks.> > Thanks for pointing this out. > > [...]