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

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Date:   Wed, 20 Sep 2023 07:36:09 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Crystal Wood <swood@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/rtmutex: Add a lockdep assert to catch
 potential nested blocking

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     45f67f30a22f264bc7a0a61255c2ee1a838e9403
Gitweb:        https://git.kernel.org/tip/45f67f30a22f264bc7a0a61255c2ee1a838e9403
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Fri, 08 Sep 2023 18:22:53 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 20 Sep 2023 09:31:14 +02:00

locking/rtmutex: Add a lockdep assert to catch potential nested blocking

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>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20230908162254.999499-7-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(+)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index a3fe05d..4a10e8c 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 c7258cb..34a5956 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 842037b..38e2924 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);
 }