Re: [net,PATCH v3 1/2] net: ks8851: Reinstate disabling of BHs around IRQ handler

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-04-16 11:26:00 [+0200], Marek Vasut wrote:
> > memory allocation. Therefore I am saying this backtrace is from an older
> > kernel.
> 
> I actually did update the backtrace in V3 with the one from next 20260413
> that contained b44596ffe1b4 ("ARM: Allow to enable RT") from
> stable-rt/v6.12-rt-rebase branch [1] .
> 
> I think I misunderstood the usage of "softirq is raised" vs. "softirq is
> invoked" above . Is it possible that there was an already raised softirq
> before the threaded IRQ handler was invoked, and __netdev_alloc_skb() is
> what invoked that softirq ?

It is not impossible. Something needs to netif_wake_queue() and
ks8851_irq() must only report IRQ_RXI (not IRQ_TXI). Then it can happen.
But usually the driver "stops" the queue if it can't process any new
packets and resumes it once a packet has been sent so it has room again.

> > If there is a flaw in my the theory please explain _how_ you managed
> > that get that backtrace. I am sure it must have from an older kernel and
> > _now_ this lockup also happens on !RT kernels (except for the SPI
> > platform).
> I used [1] , with PREEMPT_RT enabled , on stm32mp157c SoC . I ran iperf3 -s
> on the stm32 side, iperf3 -c 192.168.1.2 -t 0 --bidir on the hostpc side.
> The backtrace happened shortly after.

Hmm. Let me accept it then.

Sebastian