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

[Sebastian Andrzej Siewior]

On 2026-04-01 18:55:43 [+0200], Daniel Vacek wrote:
> > > > The above was me thinking and does not even compile for !RT. Commit
> > > > b824c3e16c190 ("net: Provide a PREEMPT_RT specific check for
> > > > netdev_queue::_xmit_lock") is what was merged in the end.
> 
> Thinking about it again, wouldn't it be better to have one generic
> solution rather then special-casing for PREEMPT_RT vs. !PREEMPT_RT?

PREEMPT_RT and !PREEMPT_RT is fundamentally different here. The one is
not preemptible and records the CPU of the lock owner to detect a
recursive deadlock.
The other is preemptible, uses a different locking type/ class which
records the lock owner which can be utilised for this purpose.

A generic thing would be to remove this and rely on lockdep. This could
work if it is only a devel thing and never "I setup something and make a
loop" sort of thing.

> --nX

Sebastian