netdev - Re: [PATCH net] net: lwtunnel: disable preemption when required

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Message-ID: <Z-62MSCyMsqtMW1N@mini-arch>
Date: Thu, 3 Apr 2025 09:24:17 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Justin Iurman <justin.iurman@...ege.be>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
	kuniyu@...zon.com,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH net] net: lwtunnel: disable preemption when required

On 04/03, Justin Iurman wrote:
> In lwtunnel_{input|output|xmit}(), dev_xmit_recursion() may be called in
> preemptible scope for PREEMPT kernels. This patch disables preemption
> before calling dev_xmit_recursion(). Preemption is re-enabled only at
> the end, since we must ensure the same CPU is used for both
> dev_xmit_recursion_inc() and dev_xmit_recursion_dec() (and any other
> recursion levels in some cases) in order to maintain valid per-cpu
> counters.

Dummy question: CONFIG_PREEMPT_RT uses current->net_xmit.recursion to
track the recursion. Any reason not to do it in the generic PREEMPT case?