linux-kernel - [PATCH v2 4/4] locking/rtmutex: Add a lockdep assert to catch potential nested blocking

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Date:   Thu, 27 Apr 2023 13:19:37 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Ben Segall <bsegall@...gle.com>, Boqun Feng <boqun.feng@...il.com>,
        Crystal Wood <swood@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        John Stultz <jstultz@...gle.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH v2 4/4] locking/rtmutex: Add a lockdep assert to catch potential nested blocking

From: Thomas Gleixner <tglx@...utronix.de>

There used to be a BUG_ON(current->pi_blocked_on) in the lock acquisition
functions, but that vanished in one of the rtmutex overhauls.

Bring it back in form of a lockdep assert to catch code paths which take
rtmutex based locks with current::pi_blocked_on != NULL.

Reported-by: Crystal Wood <swood@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 kernel/locking/rtmutex.c     | 2 ++
 kernel/locking/rwbase_rt.c   | 2 ++
 kernel/locking/spinlock_rt.c | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index dd76c1b9b7d21..479a9487edcc2 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1727,6 +1727,8 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
 static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
 					   unsigned int state)
 {
+	lockdep_assert(!current->pi_blocked_on);
+
 	if (likely(rt_mutex_try_acquire(lock)))
 		return 0;
 
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 945d474f5d27f..5be92ca5afabc 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -133,6 +133,8 @@ static __always_inline int rwbase_read_lock(struct rwbase_rt *rwb,
 {
 	int ret;
 
+	lockdep_assert(!current->pi_blocked_on);
+
 	if (rwbase_read_trylock(rwb))
 		return 0;
 
diff --git a/kernel/locking/spinlock_rt.c b/kernel/locking/spinlock_rt.c
index 62c4a6866087a..9fe282cd145d9 100644
--- a/kernel/locking/spinlock_rt.c
+++ b/kernel/locking/spinlock_rt.c
@@ -37,6 +37,8 @@
 
 static __always_inline void rtlock_lock(struct rt_mutex_base *rtm)
 {
+	lockdep_assert(!current->pi_blocked_on);
+
 	if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
 		rtlock_slowlock(rtm);
 }
-- 
2.40.1