Re: [PATCH net] netpoll: run NAPI poll in softirq context to avoid rq->lock self-deadlock

[Petr Mladek <pmladek@suse.com>]

On Wed 2026-06-17 13:15:04, Peter Zijlstra wrote:
> On Wed, Jun 17, 2026 at 12:12:07PM +0200, Petr Mladek wrote:
> > On Tue 2026-06-16 17:31:22, Sebastian Andrzej Siewior wrote:
> > > On 2026-06-16 08:11:28 [-0700], Jakub Kicinski wrote:
> > > > > 
> > > > > Adding sched and printk folks for opinions while eyeballing
> > > > > WARN_ON_DEFERRED().
> > > > 
> > > > Thanks a lot for looking into this! To be clear - the printk_deferred /
> > > > WARN_DEFERRED would be just for stable? Or there's still some
> > > > sensitivity even with nbcon?
> > > 
> > > We already have printk_deferred(). WARN_DEFERRED() would be new. I
> > > *think* this is not limited netpoll/ netconsole but all console drivers
> > > not using CON_NBCON if the printk (via WARN) occurs with the rq held.
> > > I don't remember all the details but printk_deferred() was introduced to
> > > circumvent this until printk is fixed.
> > 
> > Just to make it clear. The problem with the legacy consoles is that
> > they are called under console_lock() which is a semaphore. And it
> > calls wake_up_process() in console_unlock() when there is another
> > waiter on the lock.
> > 
> > > Once we get rid of those legacy drivers and NBCON is the default we can
> > > get rid of printk_deferred() :)
> > 
> > Yup.
> 
> Can't we push all the legacy consoles into a single legacy kthread? I
> mean, converting all consoles is of course awesome, but should we really
> wait for that?

I am afraid that converting the consoles one by one is the deal with
Linus. I could imagine to moving last few sinners into the kthread
when the majority is converted. But we are far from there :-/

Best Regards,
Petr