linux-kernel - Re: [PATCH 1/2] net: Assert proper context while calling napi

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Message-ID: <20250213-translucent-nightingale-of-upgrade-b41f2e@leitao>
Date: Thu, 13 Feb 2025 01:58:17 -0800
From: Breno Leitao <leitao@...ian.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, Hayes Wang <hayeswang@...ltek.com>,
	linux-usb@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] net: Assert proper context while calling
 napi_schedule()

On Wed, Feb 12, 2025 at 07:48:20PM -0800, Jakub Kicinski wrote:
> On Wed, 12 Feb 2025 18:43:28 +0100 Frederic Weisbecker wrote:
> > napi_schedule() is expected to be called either:
> > 
> > * From an interrupt, where raised softirqs are handled on IRQ exit
> > 
> > * From a softirq disabled section, where raised softirqs are handled on
> >   the next call to local_bh_enable().
> > 
> > * From a softirq handler, where raised softirqs are handled on the next
> >   round in do_softirq(), or further deferred to a dedicated kthread.
> > 
> > Other bare tasks context may end up ignoring the raised NET_RX vector
> > until the next random softirq handling opportunity, which may not
> > happen before a while if the CPU goes idle afterwards with the tick
> > stopped.
> > 
> > Report inappropriate calling contexts when neither of the three above
> > conditions are met.
> 
> Looks like netcons is hitting this warning in netdevsim:
> 
> [   16.063196][  T219]  nsim_start_xmit+0x4e0/0x6f0 [netdevsim]
> [   16.063219][  T219]  ? netif_skb_features+0x23e/0xa80
> [   16.063237][  T219]  netpoll_start_xmit+0x3c3/0x670
> [   16.063258][  T219]  __netpoll_send_skb+0x3e9/0x800
> [   16.063287][  T219]  netpoll_send_skb+0x2a/0xa0
> [   16.063298][  T219]  send_ext_msg_udp+0x286/0x350 [netconsole]
> [   16.063325][  T219]  write_ext_msg+0x1c6/0x230 [netconsole]
> [   16.063346][  T219]  console_emit_next_record+0x20d/0x430
> 
> https://netdev-3.bots.linux.dev/vmksft-net-drv-dbg/results/990261/7-netcons-basic-sh/stderr
> 
> We gotta fix that first.

Thanks Jakub,

I understand that it will be fixed by this patchset, right?

https://lore.kernel.org/all/20250212-netdevsim-v1-1-20ece94daae8@debian.org/