linux-kernel - [PATCH v3 1/4] srcu: Move rcu_is_watching() checks to srcu_read_{,un}lock

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Message-Id: <20250721162433.10454-1-paulmck@kernel.org>
Date: Mon, 21 Jul 2025 09:24:30 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH v3 1/4] srcu: Move rcu_is_watching() checks to srcu_read_{,un}lock_fast()

The rcu_is_watching() warnings are currently in the SRCU-tree
implementations of __srcu_read_lock_fast() and __srcu_read_unlock_fast().
However, this makes it difficult to create _notrace variants of
srcu_read_lock_fast() and srcu_read_unlock_fast().  This commit therefore
moves these checks to srcu_read_lock_fast(), srcu_read_unlock_fast(),
srcu_down_read_fast(), and srcu_up_read_fast().

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 include/linux/srcu.h     | 4 ++++
 include/linux/srcutree.h | 2 --
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index f179700fecafb..478c73d067f7d 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -275,6 +275,7 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *
 {
 	struct srcu_ctr __percpu *retval;
 
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_fast().");
 	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
 	retval = __srcu_read_lock_fast(ssp);
 	rcu_try_lock_acquire(&ssp->dep_map);
@@ -295,6 +296,7 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *
 static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *ssp) __acquires(ssp)
 {
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi());
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_down_read_fast().");
 	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
 	return __srcu_read_lock_fast(ssp);
 }
@@ -389,6 +391,7 @@ static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ct
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
 	srcu_lock_release(&ssp->dep_map);
 	__srcu_read_unlock_fast(ssp, scp);
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
 }
 
 /**
@@ -405,6 +408,7 @@ static inline void srcu_up_read_fast(struct srcu_struct *ssp, struct srcu_ctr __
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi());
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
 	__srcu_read_unlock_fast(ssp, scp);
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_up_read_fast().");
 }
 
 /**
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index bf44d8d1e69ea..043b5a67ef71e 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -244,7 +244,6 @@ static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct
 {
 	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
 
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_fast().");
 	if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))
 		this_cpu_inc(scp->srcu_locks.counter); /* Y */
 	else
@@ -275,7 +274,6 @@ static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_
 		this_cpu_inc(scp->srcu_unlocks.counter);  /* Z */
 	else
 		atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks));  /* Z */
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
 }
 
 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
-- 
2.40.1