netdev - [PATCH] net: Handle napi_schedule() calls from non-interrupt

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Message-ID: <20250221173009.21742-1-frederic@kernel.org>
Date: Fri, 21 Feb 2025 18:30:09 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	netdev@...r.kernel.org,
	Breno Leitao <leitao@...ian.org>,
	Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Francois Romieu <romieu@...zoreil.com>,
	Paul Menzel <pmenzel@...gen.mpg.de>
Subject: [PATCH] net: Handle napi_schedule() calls from non-interrupt

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.

Such "misuses" have been detected on several places thanks to messages
of the kind:

	"NOHZ tick-stop error: local softirq work is pending, handler #08!!!"

Chasing each and every misuse can be a long journey given the amount of
existing callers. Fixing them can also prove challenging if the caller
may be called from different kind of context.

Therefore fix this from napi_schedule() itself with waking up ksoftirqd
when softirqs are raised from task contexts.

Reported-by: Paul Menzel <pmenzel@...gen.mpg.de>
Closes: 354a2690-9bbf-4ccb-8769-fa94707a9340@...gen.mpg.de
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index c0021cbd28fc..2419cc558a64 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4692,7 +4692,7 @@ static inline void ____napi_schedule(struct softnet_data *sd,
 	 * we have to raise NET_RX_SOFTIRQ.
 	 */
 	if (!sd->in_net_rx_action)
-		__raise_softirq_irqoff(NET_RX_SOFTIRQ);
+		raise_softirq_irqoff(NET_RX_SOFTIRQ);
 }

 #ifdef CONFIG_RPS
-- 
2.48.1