From 6b596e62ed9f90c4a97e68ae1f7b1af5beeb3c05 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 8 Sep 2023 18:22:51 +0200 Subject: sched: Provide rt_mutex specific scheduler helpers With PREEMPT_RT there is a rt_mutex recursion problem where sched_submit_work() can use an rtlock (aka spinlock_t). More specifically what happens is: mutex_lock() /* really rt_mutex */ ... __rt_mutex_slowlock_locked() task_blocks_on_rt_mutex() // enqueue current task as waiter // do PI chain walk rt_mutex_slowlock_block() schedule() sched_submit_work() ... spin_lock() /* really rtlock */ ... __rt_mutex_slowlock_locked() task_blocks_on_rt_mutex() // enqueue current task as waiter *AGAIN* // *CONFUSION* Fix this by making rt_mutex do the sched_submit_work() early, before it enqueues itself as a waiter -- before it even knows *if* it will wait. [[ basically Thomas' patch but with different naming and a few asserts added ]] Originally-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/20230908162254.999499-5-bigeasy@linutronix.de --- include/linux/sched/rt.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux/sched') diff --git a/include/linux/sched/rt.h b/include/linux/sched/rt.h index 994c25640e15..b2b9e6eb9683 100644 --- a/include/linux/sched/rt.h +++ b/include/linux/sched/rt.h @@ -30,6 +30,10 @@ static inline bool task_is_realtime(struct task_struct *tsk) } #ifdef CONFIG_RT_MUTEXES +extern void rt_mutex_pre_schedule(void); +extern void rt_mutex_schedule(void); +extern void rt_mutex_post_schedule(void); + /* * Must hold either p->pi_lock or task_rq(p)->lock. */ -- cgit v1.3