linux-kernel - [PATCH tip/core/rcu 15/17] rcu: Simplify rcu_eqs

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Date:   Fri,  1 Dec 2017 11:36:46 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 15/17] rcu: Simplify rcu_eqs_{enter,exit}() non-idle task debug code

The code that checks for non-idle non-nohz_idle-usermode tasks invoking
rcu_eqs_enter() and rcu_eqs_exit() prints a considerable quantity of
helpful information.  However, these checks fire rarely, so the extra
complexity is no longer worth it.  This commit therefore replaces this
debug code with simple WARN_ON_ONCE() statements.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/trace/events/rcu.h | 12 +++++-------
 kernel/rcu/tree.c          | 24 ++----------------------
 2 files changed, 7 insertions(+), 29 deletions(-)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index d103de9f8c10..adf47c635c8e 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -424,15 +424,13 @@ TRACE_EVENT(rcu_fqs,
  * as argument: "Start" for entering dyntick-idle mode, "Startirq" for
  * entering it from irq/NMI, "End" for leaving it, "Endirq" for leaving it
  * to irq/NMI, "--=" for events moving towards idle, and "++=" for events
- * moving away from idle.  "Error on entry: not idle task" and "Error
- * on exit: not idle task" indicate that a non-idle task is erroneously
- * toying with the idle loop.
+ * moving away from idle.
  *
  * These events also take a pair of numbers, which indicate the nesting
- * depth before and after the event of interest.  Note that task-related
- * and interrupt-related events use two separate counters, and that the
- * "++=" and "--=" events for irq/NMI will change the counter by two,
- * otherwise by one.
+ * depth before and after the event of interest, and a third number that is
+ * the ->dynticks counter.  Note that task-related and interrupt-related
+ * events use two separate counters, and that the "++=" and "--=" events
+ * for irq/NMI will change the counter by two, otherwise by one.
  */
 TRACE_EVENT(rcu_dyntick,
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 46a8e06bf03e..4d374d2bc925 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -773,17 +773,7 @@ static void rcu_eqs_enter(bool user)
 
 	lockdep_assert_irqs_disabled();
 	trace_rcu_dyntick(TPS("Start"), rdtp->dynticks_nesting, 0, rdtp->dynticks);
-	if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
-	    !user && !is_idle_task(current)) {
-		struct task_struct *idle __maybe_unused =
-			idle_task(smp_processor_id());
-
-		trace_rcu_dyntick(TPS("Error on entry: not idle task"), rdtp->dynticks_nesting, 0, rdtp->dynticks);
-		rcu_ftrace_dump(DUMP_ORIG);
-		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
-			  current->pid, current->comm,
-			  idle->pid, idle->comm); /* must be idle task! */
-	}
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
 	for_each_rcu_flavor(rsp) {
 		rdp = this_cpu_ptr(rsp->rda);
 		do_nocb_deferred_wakeup(rdp);
@@ -941,17 +931,7 @@ static void rcu_eqs_exit(bool user)
 	rcu_dynticks_eqs_exit();
 	rcu_cleanup_after_idle();
 	trace_rcu_dyntick(TPS("End"), rdtp->dynticks_nesting, 1, rdtp->dynticks);
-	if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
-	    !user && !is_idle_task(current)) {
-		struct task_struct *idle __maybe_unused =
-			idle_task(smp_processor_id());
-
-		trace_rcu_dyntick(TPS("Error on exit: not idle task"), rdtp->dynticks_nesting, 1, rdtp->dynticks);
-		rcu_ftrace_dump(DUMP_ORIG);
-		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
-			  current->pid, current->comm,
-			  idle->pid, idle->comm); /* must be idle task! */
-	}
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
 	WRITE_ONCE(rdtp->dynticks_nesting, 1);
 	WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
 }
-- 
2.5.2