Re: [PATCH net v6] usbnet: fix smp_processor_id() use in preemptible context

[Alan Stern]

On Wed, Oct 07, 2026 at 08:00:49PM -0700, Jakub Kicinski wrote:
> On Mon,  5 Oct 2026 00:59:25 +0300 Ömer Mete Kaya wrote:
> > tx_complete() calls this_cpu_ptr() before disabling preemption, which
> > triggers a BUG when running with CONFIG_DEBUG_PREEMPT:
> > 
> >   BUG: using smp_processor_id() in preemptible code in tx_complete
> > 
> > Fix by using get_cpu_ptr()/put_cpu_ptr() which disable preemption and
> > return the per-CPU pointer atomically. The usbnet_skb_return() hunk
> > is a hardening change: that path runs in softirq context so no warning
> > fires there, but the same fix is applied for consistency.
> 
> This looks odd, how did we miss this for 8 years.
> 
> Greg is probably busy, but would be good to get a confirmation
> from either him or some other USB expert that the callbacks
> can indeed be called in process context.

They can be called in BH context with interrupts enabled.  Is that close 
enough?

Alan Stern