linux-kernel - [PATCH 2/2] r8152: Call napi_schedule() from proper context

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Message-ID: <20250212174329.53793-3-frederic@kernel.org>
Date: Wed, 12 Feb 2025 18:43:29 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Hayes Wang <hayeswang@...ltek.com>,
	linux-usb@...r.kernel.org,
	netdev@...r.kernel.org,
	Paul Menzel <pmenzel@...gen.mpg.de>
Subject: [PATCH 2/2] r8152: Call napi_schedule() from proper context

napi_schedule() is expected to be called either:

* From an interrupt, where raised softirqs are handled on IRQ exit

* Fom 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.

r8152 may call napi_schedule() on device resume time from a bare task
context without disabling softirqs as the following trace shows:

	__raise_softirq_irqoff
	__napi_schedule
	rtl8152_runtime_resume.isra.0
	rtl8152_resume
	usb_resume_interface.isra.0
	usb_resume_both
	__rpm_callback
	rpm_callback
	rpm_resume
	__pm_runtime_resume
	usb_autoresume_device
	usb_remote_wakeup
	hub_event
	process_one_work
	worker_thread
	kthread
	ret_from_fork
	ret_from_fork_asm

This may result in the NET_RX softirq vector to be ignored until the
next interrupt or softirq handling. The delay can be long if the
above kthread leaves the CPU idle and the tick is stopped for a while,
as reported with the following message:

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

Fix this with disabling softirqs while calling napi_schedule(). The
call to local_bh_enable() will take care of the NET_RX raised vector.

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>
---
 drivers/net/usb/r8152.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
index 468c73974046..1325460ae457 100644
--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -8537,8 +8537,11 @@ static int rtl8152_runtime_resume(struct r8152 *tp)
 		clear_bit(SELECTIVE_SUSPEND, &tp->flags);
 		smp_mb__after_atomic();
 
-		if (!list_empty(&tp->rx_done))
+		if (!list_empty(&tp->rx_done)) {
+			local_bh_disable();
 			napi_schedule(&tp->napi);
+			local_bh_enable();
+		}
 
 		usb_submit_urb(tp->intr_urb, GFP_NOIO);
 	} else {
-- 
2.46.0