Re: [PATCH net v2 1/2] netpoll: use a raw lock for the deferred transmit queue
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: 2026-10-01 07:48:22
Also in:
linux-rt-devel, lkml, stable
On 2026-09-30 21:21:02 [+0200], Karl Mehltretter wrote:
netpoll_send_skb() calls __netpoll_send_skb() with hard interrupts disabled. When direct transmission cannot complete, the latter queues the skb with skb_queue_tail(). The sk_buff_head lock may sleep on PREEMPT_RT: BUG: sleeping function called from invalid context in_atomic(): 0, irqs_disabled(): 1, non_block: 0 rt_spin_lock skb_queue_tail netpoll_send_skb
How is this possible? netpoll is only used by netconsole right? And this is CON_NBCON so it only prints threaded. What is the missing piece?
The delayed transmit worker has the same problem when it requeues a busy
skb with skb_queue_head() after disabling interrupts.
Add a dedicated raw spinlock and use the unlocked skb queue helpers under
it. Keep raw critical sections limited to queue operations. During
cleanup, splice the queue to a private list before freeing its skbs.
Fixes: b6cd27ed3388 ("netpoll per device txq")
Cc: stable@vger.kernel.org # 6.12+
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <redacted>Sebastian