Subject: [PATCH 1/2] net: Assert proper context while calling napi_schedule()

From: Frederic Weisbecker <[email-masked]>
Date: Wed, 12 Feb 2025 18:43:28 +0100

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.

Report inappropriate calling contexts when neither of the three above
conditions are met.

Signed-off-by: Frederic Weisbecker <[email-masked]>
---
 include/linux/lockdep.h | 12 ++++++++++++
 net/core/dev.c          |  1 +
 2 files changed, 13 insertions(+)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 67964dc4db95..1bd730b881f0 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -619,6 +619,17 @@ do {									\
 		     (!in_softirq() || in_irq() || in_nmi()));		\
 } while (0)
 
+/*
+ * Assert to be either in hardirq or in serving softirq or with
+ * softirqs disabled. Verifies a safe context to queue a softirq
+ * with __raise_softirq_irqoff().
+ */
+#define lockdep_assert_in_interrupt()				\
+do {								\
+	WARN_ON_ONCE(__lockdep_enabled && !in_interrupt());	\
+} while (0)
+
+
 extern void lockdep_assert_in_softirq_func(void);
 
 #else
@@ -634,6 +645,7 @@ extern void lockdep_assert_in_softirq_func(void);
 # define lockdep_assert_preemption_enabled() do { } while (0)
 # define lockdep_assert_preemption_disabled() do { } while (0)
 # define lockdep_assert_in_softirq() do { } while (0)
+# define lockdep_assert_in_interrupt() do { } while (0)
 # define lockdep_assert_in_softirq_func() do { } while (0)
 #endif
 
diff --git a/net/core/dev.c b/net/core/dev.c
index c0021cbd28fc..80e415ccf2c8 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4666,6 +4666,7 @@ static inline void ____napi_schedule(struct softnet_data *sd,
 	struct task_struct *thread;
 
 	lockdep_assert_irqs_disabled();
+	lockdep_assert_in_interrupt();
 
 	if (test_bit(NAPI_STATE_THREADED, &napi->state)) {
 		/* Paired with smp_mb__before_atomic() in
-- 
2.46.0