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

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Message-ID: <20230815111430.488430699@infradead.org>
Date:   Tue, 15 Aug 2023 13:01:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     bigeasy@...utronix.de, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        bsegall@...gle.com, boqun.feng@...il.com, swood@...hat.com,
        bristot@...hat.com, dietmar.eggemann@....com, mingo@...hat.com,
        jstultz@...gle.com, juri.lelli@...hat.com, mgorman@...e.de,
        rostedt@...dmis.org, vschneid@...hat.com,
        vincent.guittot@...aro.org, longman@...hat.com, will@...nel.org
Subject: [PATCH 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: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20230427111937.2745231-5-bigeasy@linutronix.de
---
 kernel/locking/rtmutex.c     |    2 ++
 kernel/locking/rwbase_rt.c   |    2 ++
 kernel/locking/spinlock_rt.c |    2 ++
 3 files changed, 6 insertions(+)

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1774,6 +1774,8 @@ static int __sched rt_mutex_slowlock(str
 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;
 
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -131,6 +131,8 @@ static int __sched __rwbase_read_lock(st
 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;
 
--- 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);
 }