linux-kernel - [PATCH v2 6/6] locking/rtmutex: Add a lockdep assert to catch potential nested blocking

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Message-Id: <20230825181033.504534-7-bigeasy@linutronix.de>
Date:   Fri, 25 Aug 2023 20:10:33 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Cc:     bigeasy@...utronix.de, tglx@...utronix.de, boqun.feng@...il.com,
        bristot@...hat.com, bsegall@...gle.com, dietmar.eggemann@....com,
        jstultz@...gle.com, juri.lelli@...hat.com, longman@...hat.com,
        mgorman@...e.de, mingo@...hat.com, rostedt@...dmis.org,
        swood@...hat.com, vincent.guittot@...aro.org, vschneid@...hat.com,
        will@...nel.org
Subject: [PATCH v2 6/6] 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: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20230427111937.2745231-5-bigeasy@linutronix.de
Link: https://lore.kernel.org/r/20230815111430.488430699@infradead.org
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 a3fe05dfd0d8f..4a10e8c16fd2b 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1784,6 +1784,8 @@ 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 7d57bfb909001..b5e881250fec5 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -133,6 +133,8 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
 static __always_inline int rwbase_read_lock(struct rwbase_rt *rwb,
 					    unsigned int state)
 {
+	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 842037b2ba548..38e292454fccb 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