linux-kernel - [patch 14/14] locking/rtmutex: Restrict the trylock WARN

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Date:   Tue, 23 Mar 2021 22:30:33 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [patch 14/14] locking/rtmutex: Restrict the trylock WARN_ON() to debug

The warning as written is expensive and not really required for a
production kernel. Make it depend on rt mutex debugging and use !in_task()
for the condition which generates far better code and gives the same
answer.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/locking/rtmutex.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1445,9 +1445,8 @@ EXPORT_SYMBOL_GPL(rt_mutex_lock_interrup
  *
  * @lock:	the rt_mutex to be locked
  *
- * This function can only be called in thread context. It's safe to
- * call it from atomic regions, but not from hard interrupt or soft
- * interrupt context.
+ * This function can only be called in thread context. It's safe to call it
+ * from atomic regions, but not from hard or soft interrupt context.
  *
  * Returns 1 on success and 0 on contention
  */
@@ -1455,7 +1454,7 @@ int __sched rt_mutex_trylock(struct rt_m
 {
 	int ret;
 
-	if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
+	if (IS_ENABLED(CONFIG_RT_MUTEX_DEBUG) && WARN_ON_ONCE(!in_task()))
 		return 0;
 
 	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))