From: Jakub Kicinski <kuba@kernel.org>
To: Jiayuan Chen <jiayuan.chen@linux.dev>,
Eric Dumazet <edumazet@google.com>
Cc: netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
David Ahern <dsahern@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Simon Horman <horms@kernel.org>,
Weiming Shi <bestswngs@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net v2] net: fix __this_cpu_add() in preemptible code in dev_xmit_recursion_inc/dec
Date: Sun, 12 Apr 2026 09:33:48 -0700 [thread overview]
Message-ID: <20260412093348.45ce45b0@kernel.org> (raw)
In-Reply-To: <20260410020631.191786-1-jiayuan.chen@linux.dev>
On Fri, 10 Apr 2026 10:06:30 +0800 Jiayuan Chen wrote:
> dev_xmit_recursion_{inc,dec}() use __this_cpu_{inc,dec}() which requires
> the caller to be non-preemptible in order to avoid cpu migration. However,
> some callers like SCTP's UDP encapsulation path invoke iptunnel_xmit()
> from process context without disabling BH or preemption:
>
> sctp_inet_connect -> __sctp_connect -> sctp_do_sm ->
> sctp_outq_flush -> sctp_packet_transmit -> sctp_v4_xmit ->
> udp_tunnel_xmit_skb -> iptunnel_xmit -> dev_xmit_recursion_inc
Eric, weren't there also a bunch of RCU reports because of this path?
Should we perhaps take the RCU read lock here?
> + guard(migrate)();
Sorry but I detest the guard() usage. Please use migrate_disable()
Quoting documentation:
Use of ``guard()`` is discouraged within any function longer than 20
lines, ``scoped_guard()`` is considered more readable. Using normal
lock/unlock is still (weakly) preferred.
See:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html#using-device-managed-and-cleanup-h-constructs
prev parent reply other threads:[~2026-04-12 16:33 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-10 2:06 [PATCH net v2] net: fix __this_cpu_add() in preemptible code in dev_xmit_recursion_inc/dec Jiayuan Chen
2026-04-10 8:55 ` Eric Dumazet
2026-04-12 16:33 ` Jakub Kicinski [this message]
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