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 01:14:35 [+0200], Marek Vasut wrote:
> > spin_unlock_bh(&ks->statelock)? After that unlock, the softirq must be
> > processed and __netdev_alloc_skb() _could_ observe pending softirqs but
> > not from ks8851.
> Because __netdev_alloc_skb() also enables/disables BH , see the "else"

Yes. But there is no softirq raised in that part. That softirq is raised
by netif_wake_queue() within a bh disabled section. Therefore upon the
unlock the softirq must be invoked.
After that, rhe allocation later on may invoke softirqs which were
raised but I don't see how ks8851 can be part of it.
Before commit 0913ec336a6c0 ("net: ks8851: Fix deadlock with the SPI
chip variant") there was no _bh around it meaning the softirq was raised
but not invoked immediately. This happened on the bh unlock during
memory allocation. Therefore I am saying this backtrace is from an older
kernel.

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).

Sebastian