From: Thomas Gleixner Date: Fri, 8 Sep 2023 18:22:53 +0200 Subject: [PATCH 6/7] locking/rtmutex: Add a lockdep assert to catch potential nested blocking Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz 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 Signed-off-by: Thomas Gleixner Signed-off-by: "Peter Zijlstra (Intel)" Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) 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(+) --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1784,6 +1784,8 @@ 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 @@ -133,6 +133,8 @@ 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); }