linux-kernel - Re: [PATCH net-next v3 4/4] netdevsim: account dropped packet length in stats on queue free

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Message-ID: <20250617064811.0d4e1490@kernel.org>
Date: Tue, 17 Jun 2025 06:48:11 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, David Wei <dw@...idwei.uk>, Shuah Khan
 <shuah@...nel.org>, Simon Horman <horms@...nel.org>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, gustavold@...il.com
Subject: Re: [PATCH net-next v3 4/4] netdevsim: account dropped packet
 length in stats on queue free

On Tue, 17 Jun 2025 06:24:23 -0700 Breno Leitao wrote:
> > here we are in process context and debug checks complain about the use
> > of this_cpu_ptr(). Let's wrap this in local_bh_disable() / enable() ?  
> 
> Thanks. I was able to reproduce it. Your suggestion avoids the complain.
> I suppose we should just wrap dev_dstats_rx_dropped_add(), right?

I think so. I hope that makes the preempt checker happy.
The reason for bh_disable rather than preempt_disable() is that we 
should only update the stats from one context, the NAPI poll context.
So we also need to prevent races with another NAPI running on the same
core while we free an old queue.