From: Thomas Gleixner <tglx@linutronix.de> Date: Thu, 27 Apr 2023 13:19:37 +0200 Subject: [PATCH 4/4] 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@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://lore.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(+) Index: linux-6.3.0-rt11/kernel/locking/rtmutex.c =================================================================== @ linux-6.3.0-rt11/kernel/locking/rtmutex.c:1730 @ 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; Index: linux-6.3.0-rt11/kernel/locking/rwbase_rt.c =================================================================== --- linux-6.3.0-rt11.orig/kernel/locking/rwbase_rt.c +++ linux-6.3.0-rt11/kernel/locking/rwbase_rt.c @ linux-6.3.0-rt11/kernel/locking/rtmutex.c:136 @ static __always_inline int rwbase_read_l { int ret; + lockdep_assert(!current->pi_blocked_on); + if (rwbase_read_trylock(rwb)) return 0; Index: linux-6.3.0-rt11/kernel/locking/spinlock_rt.c =================================================================== --- linux-6.3.0-rt11.orig/kernel/locking/spinlock_rt.c +++ linux-6.3.0-rt11/kernel/locking/spinlock_rt.c @ linux-6.3.0-rt11/kernel/locking/rtmutex.c:40 @ 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); }