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

Peter Zijlstra
2023-08-15T11:18:06Z

From: Thomas Gleixner <tglx@linutronix.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@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.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);
}