linux-kernel - [PATCH 06/34] context_tracking: Remove rcu_task_trace_heavyweight

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Message-Id: <20250923142036.112290-6-paulmck@kernel.org>
Date: Tue, 23 Sep 2025 07:20:08 -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>,
	Frederic Weisbecker <frederic@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	bpf@...r.kernel.org
Subject: [PATCH 06/34] context_tracking: Remove rcu_task_trace_heavyweight_{enter,exit}()

Because SRCU-fast does not use IPIs for its grace periods, there is
no need for real-time workloads to switch to an IPI-free mode, and
there is in turn no need for either rcu_task_trace_heavyweight_enter()
or rcu_task_trace_heavyweight_exit().  This commit therefore removes them.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: <bpf@...r.kernel.org>
---
 kernel/context_tracking.c | 20 --------------------
 1 file changed, 20 deletions(-)

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index fb5be6e9b423f2..a743e7ffa6c00f 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -54,24 +54,6 @@ static __always_inline void rcu_task_enter(void)
 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
 }
 
-/* Turn on heavyweight RCU tasks trace readers on kernel exit. */
-static __always_inline void rcu_task_trace_heavyweight_enter(void)
-{
-#ifdef CONFIG_TASKS_TRACE_RCU
-	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
-		current->trc_reader_special.b.need_mb = true;
-#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
-}
-
-/* Turn off heavyweight RCU tasks trace readers on kernel entry. */
-static __always_inline void rcu_task_trace_heavyweight_exit(void)
-{
-#ifdef CONFIG_TASKS_TRACE_RCU
-	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
-		current->trc_reader_special.b.need_mb = false;
-#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
-}
-
 /*
  * Record entry into an extended quiescent state.  This is only to be
  * called when not already in an extended quiescent state, that is,
@@ -85,7 +67,6 @@ static noinstr void ct_kernel_exit_state(int offset)
 	 * critical sections, and we also must force ordering with the
 	 * next idle sojourn.
 	 */
-	rcu_task_trace_heavyweight_enter();  // Before CT state update!
 	// RCU is still watching.  Better not be in extended quiescent state!
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !rcu_is_watching_curr_cpu());
 	(void)ct_state_inc(offset);
@@ -108,7 +89,6 @@ static noinstr void ct_kernel_enter_state(int offset)
 	 */
 	seq = ct_state_inc(offset);
 	// RCU is now watching.  Better not be in an extended quiescent state!
-	rcu_task_trace_heavyweight_exit();  // After CT state update!
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & CT_RCU_WATCHING));
 }
 
-- 
2.40.1