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

[Marek Vasut <marex@nabladev.com>]

On 4/16/26 12:48 PM, Sebastian Andrzej Siewior wrote:
> 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.
This driver .start_xmit is very simple, if there is space in the 6 kiB 
TX FIFO, then the packet is written into it, otherwise the .start_xmit 
returns NETDEV_TX_BUSY . There does not seem to be any 
netif_{start,stop,wake}_queue() in the .start_xmit path.