possible deadlock due to irq_set_thread_affinity() calling into the scheduler (was Re: [PATCH v3 38/62] KVM: SVM: Take and hold ir_list_lock across IRTE updates in IOMMU)

[Paolo Bonzini]

On Thu, Jan 22, 2026 at 7:47 PM Thomas Gleixner <tglx at kernel.org> wrote:
>
> On Wed, Jan 21 2026 at 19:13, Paolo Bonzini wrote:
> > On 1/8/26 22:53, Thomas Gleixner wrote:
> >> Are you still claiming that this is a kernel/irq bug?
> >
> > Not really, I did say I'd like to treat it as a kernel/irq bug...
> > but certainly didn't have hopes high enough to "claim" that.
> > I do think that it's ugly to have locks that are internal,
> > non-leaf and held around callbacks; but people smarter than
> > me have thought about it and you can't call it a bug anyway.
>
> Deep core code has a tendency to be ugly. But if it makes your life
> easier, then these wakeups can be delayed via an irq_work to be outside
> of the lock. That needs some life-time issues to be addressed, but
> should be doable.

Thanks for the suggestion---hopefully it's not needed at all and we
can delay taking the lock in KVM.

Paolo