Re: "Dead loop on virtual device" error without softirq-BKL on PREEMPT_RT

[Daniel Vacek]

On Thu, 2 Apr 2026 at 10:31, Sebastian Andrzej Siewior
<bigeasy@xxxxxxxxxxxxx> wrote:
> On 2026-04-02 09:50:35 [+0200], Daniel Vacek wrote:
> > My idea was that the non-preemptible one can record `current` task
> > instead of the CPU to detect the deadlock. And that would also work
> > for the preemptible case (it would actually match the lock owner
> > approach as you did for the PREEMPT_RT case).
> > One code for both configurations, no special-casing. I'd argue that's
> > a better result. Am I missing something?
> >
> > The size of the netdev_queue structure would grow by 8 bytes for !RT
> > case, but that's not a big deal, IMO. For RT case it would just fill
> > the hole.
>
> We have xmit_lock_owner as int. If you replace it with task_struct *
> then on 64bit the size of the struct netdev_queue will remain unchanged
> as it fills the hole before the following long.
> Then you could record `current' as the lock owner in both cases. This
> should work.

Well, that's the patch I originally sent then.

https://lore.kernel.org/linux-rt-devel/20260318103009.2120920-1-neelx@xxxxxxxx/

--nX

>
> Sebastian