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From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	mingo@kernel.org, jiangshanlai@gmail.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 04/13] rcu-tasks: Remove second argument of rcu_read_unlock_trace_special()
Date: Wed, 15 Sep 2021 16:45:55 -0700	[thread overview]
Message-ID: <20210915234604.3907802-4-paulmck@kernel.org> (raw)
In-Reply-To: <20210915234538.GA3907674@paulmck-ThinkPad-P17-Gen-1>

The second argument of rcu_read_unlock_trace_special() is always zero.
When called from exit_tasks_rcu_finish_trace(), it is the constant
zero, and rcu_read_unlock_trace_special() doesn't get called from
rcu_read_unlock_trace() unless the value of local variable "nesting"
is zero because in that case the early return is taken instead.

This commit therefore removes the "nesting" argument from the
rcu_read_unlock_trace_special() function, substituting the constant
zero within that function.  This commit also adds a WARN_ON_ONCE()
to rcu_read_lock_trace_held() in case non-zeroness some day appears.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/rcupdate_trace.h | 5 +++--
 kernel/rcu/tasks.h             | 6 +++---
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h
index 86c8f6c98412..6f9c35817398 100644
--- a/include/linux/rcupdate_trace.h
+++ b/include/linux/rcupdate_trace.h
@@ -31,7 +31,7 @@ static inline int rcu_read_lock_trace_held(void)
 
 #ifdef CONFIG_TASKS_TRACE_RCU
 
-void rcu_read_unlock_trace_special(struct task_struct *t, int nesting);
+void rcu_read_unlock_trace_special(struct task_struct *t);
 
 /**
  * rcu_read_lock_trace - mark beginning of RCU-trace read-side critical section
@@ -80,7 +80,8 @@ static inline void rcu_read_unlock_trace(void)
 		WRITE_ONCE(t->trc_reader_nesting, nesting);
 		return;  // We assume shallow reader nesting.
 	}
-	rcu_read_unlock_trace_special(t, nesting);
+	WARN_ON_ONCE(nesting != 0);
+	rcu_read_unlock_trace_special(t);
 }
 
 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 8387e70e6b00..a3f4f9bd8c67 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -848,7 +848,7 @@ static void rcu_read_unlock_iw(struct irq_work *iwp)
 static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw);
 
 /* If we are the last reader, wake up the grace-period kthread. */
-void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
+void rcu_read_unlock_trace_special(struct task_struct *t)
 {
 	int nq = READ_ONCE(t->trc_reader_special.b.need_qs);
 
@@ -858,7 +858,7 @@ void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
 	// Update .need_qs before ->trc_reader_nesting for irq/NMI handlers.
 	if (nq)
 		WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
-	WRITE_ONCE(t->trc_reader_nesting, nesting);
+	WRITE_ONCE(t->trc_reader_nesting, 0);
 	if (nq && atomic_dec_and_test(&trc_n_readers_need_end))
 		irq_work_queue(&rcu_tasks_trace_iw);
 }
@@ -1200,7 +1200,7 @@ static void exit_tasks_rcu_finish_trace(struct task_struct *t)
 	WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));
 	WRITE_ONCE(t->trc_reader_nesting, 0);
 	if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)))
-		rcu_read_unlock_trace_special(t, 0);
+		rcu_read_unlock_trace_special(t);
 }
 
 /**
-- 
2.31.1.189.g2e36527f23


  parent reply	other threads:[~2021-09-15 23:46 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-15 23:45 [PATCH rcu 0/13] Tasks RCU updates for v5.16 Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 01/13] rcu-tasks: Wait for trc_read_check_handler() IPIs Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 02/13] rcu-tasks: Simplify trc_read_check_handler() atomic operations Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 03/13] rcu-tasks: Add trc_inspect_reader() checks for exiting critical section Paul E. McKenney
2021-09-15 23:45 ` Paul E. McKenney [this message]
2021-09-15 23:45 ` [PATCH rcu 05/13] rcu-tasks: Fix s/instruction/instructions/ typo in comment Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 06/13] rcu-tasks: Move RTGS_WAIT_CBS to beginning of rcu_tasks_kthread() loop Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 07/13] rcu-tasks: Fix s/rcu_add_holdout/trc_add_holdout/ typo in comment Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 08/13] rcu-tasks: Correct firstreport usage in check_all_holdout_tasks_trace Paul E. McKenney
2021-09-15 23:46 ` [PATCH rcu 09/13] rcu-tasks: Correct comparisons for CPU numbers in show_stalled_task_trace Paul E. McKenney
2021-09-15 23:46 ` [PATCH rcu 10/13] rcu-tasks: Clarify read side section info for rcu_tasks_rude GP primitives Paul E. McKenney
2021-09-15 23:46 ` [PATCH rcu 11/13] rcu-tasks: Fix read-side primitives comment for call_rcu_tasks_trace Paul E. McKenney
2021-09-15 23:46 ` [PATCH rcu 12/13] rcu-tasks: Fix IPI failure handling in trc_wait_for_one_reader Paul E. McKenney
2021-09-15 23:46 ` [PATCH rcu 13/13] rcu-tasks: Update comments to cond_resched_tasks_rcu_qs() Paul E. McKenney

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