From: Jakub Kicinski <kuba@kernel.org>
To: Breno Leitao <leitao@debian.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Petr Mladek <pmladek@suse.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
John Ogness <john.ogness@linutronix.de>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Vlad Poenaru <vlad.wing@gmail.com>,
Thomas Gleixner <tglx@kernel.org>,
netdev@vger.kernel.org, "David S . Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>,
Clark Williams <clrkwllms@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
linux-rt-devel@lists.linux.dev, linux-kernel@vger.kernel.org,
stable@vger.kernel.org, Frederic Weisbecker <frederic@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
K Prateek Nayak <kprateek.nayak@amd.com>
Subject: Re: [PATCH net] netpoll: run NAPI poll in softirq context to avoid rq->lock self-deadlock
Date: Wed, 17 Jun 2026 13:21:27 -0700 [thread overview]
Message-ID: <20260617132127.645534d1@kernel.org> (raw)
In-Reply-To: <ajKi4wtA8U1iZkMD@gmail.com>
On Wed, 17 Jun 2026 07:56:50 -0700 Breno Leitao wrote:
> As far as I can tell, there isn't a network driver today whose transmit
> path is completely lockless, so, even if we make netpoll lockless.
>
> It's unlikely any NIC will ever achieve this, given that NIC TX
> fundamentally relies on a shared DMA ring and doorbell register, which
> inherently cannot be made lockless.
The lock which protects the queue is maintained by the stack,
and we trylock it. Maybe I lost the thread but if you're saying
that writes to netconsole are impossible from arbitrary context,
that is _not_ true, AFAIU. We can queue a packet and kick off
the transfer on well-behaved drivers.
Main problem is the opportunistic freeing up of the queue space.
If we could avoid that in atomic context I think we'd be good.
prev parent reply other threads:[~2026-06-17 20:21 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-10 18:36 [PATCH net] netpoll: run NAPI poll in softirq context to avoid rq->lock self-deadlock Vlad Poenaru
2026-06-11 18:36 ` sashiko-bot
2026-06-12 2:11 ` Jakub Kicinski
2026-06-15 13:56 ` Sebastian Andrzej Siewior
2026-06-16 10:35 ` Sebastian Andrzej Siewior
2026-06-16 15:11 ` Jakub Kicinski
2026-06-16 15:31 ` Sebastian Andrzej Siewior
2026-06-17 10:12 ` Petr Mladek
2026-06-17 11:15 ` Peter Zijlstra
2026-06-17 11:59 ` Petr Mladek
2026-06-17 12:12 ` John Ogness
2026-06-16 16:32 ` Breno Leitao
2026-06-17 7:42 ` John Ogness
2026-06-16 17:02 ` Peter Zijlstra
2026-06-16 21:17 ` Jakub Kicinski
2026-06-17 10:37 ` Petr Mladek
2026-06-17 11:19 ` Peter Zijlstra
2026-06-17 12:13 ` Petr Mladek
2026-06-17 14:56 ` Breno Leitao
2026-06-17 17:07 ` John Ogness
2026-06-17 20:21 ` Jakub Kicinski [this message]
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