Re: [PATCH net v2 1/2] netpoll: use a raw lock for the deferred transmit queue

[Breno Leitao <leitao@debian.org>]

Hello Sebastian,

On Fri, Oct 09, 2026 at 05:52:25PM +0200, Sebastian Andrzej Siewior wrote:
> I would suggest to untangle that local-irq-disable assumption. Then we
> end up with the ::write_atomic callback on PREEMPT_RT which will raise
> warnings. But those will appear only on panic() and as the last console
> due to CON_NBCON_ATOMIC_UNSAFE so everything will go according to the
> plan.
> On !RT the whole __netpoll_send_skb() will be with disabled interrupts
> due to the console lock. On RT it won't and I don't know if anything
> down the call chain assumes that.

Thanks for the patch, On PREEMPT_RT, the send path is clean.
all the selftest I have are passing fine, without a single splat, while
the unpatched kernel produces about a dozen over the same tests. 

On !RT, the first message triggers, but it doesn't seem a big deal.

  WARNING: kernel/softirq.c:453 at __local_bh_enable_ip+0x118/0x120, CPU#4: pr/netcons_netc/307
  ...
  Call trace:
   __local_bh_enable_ip+0x118/0x120 (P)
   netpoll_send_skb+0x1a8/0x364
   send_udp+0x348/0x4a8
   netconsole_write+0x16c/0x628
   nbcon_emit_next_record+0x150/0x3cc
   nbcon_emit_one+0x74/0x158
   nbcon_kthread_func+0x18c/0x258
   kthread+0x108/0x134

Anyway, is this patch something you are planning to send officially?

Thanks,
--breno