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

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Message-ID: <20250212194820.059dac6f@kernel.org>
Date: Wed, 12 Feb 2025 19:48:20 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: 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, Breno Leitao
 <leitao@...ian.org>
Subject: Re: [PATCH 1/2] net: Assert proper context while calling
 napi_schedule()

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.

Please post the fixes for net, and then the warning in net-next.
So that we have some time to fix the uncovered warnings before
users are broadly exposed to them.
-- 
pw-bot: cr