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6b596e62ed
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 <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230908162254.999499-5-bigeasy@linutronix.de
64 lines
1.3 KiB
C
64 lines
1.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_SCHED_RT_H
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#define _LINUX_SCHED_RT_H
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#include <linux/sched.h>
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struct task_struct;
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static inline int rt_prio(int prio)
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{
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if (unlikely(prio < MAX_RT_PRIO))
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return 1;
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return 0;
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}
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static inline int rt_task(struct task_struct *p)
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{
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return rt_prio(p->prio);
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}
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static inline bool task_is_realtime(struct task_struct *tsk)
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{
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int policy = tsk->policy;
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if (policy == SCHED_FIFO || policy == SCHED_RR)
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return true;
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if (policy == SCHED_DEADLINE)
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return true;
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return false;
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}
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#ifdef CONFIG_RT_MUTEXES
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extern void rt_mutex_pre_schedule(void);
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extern void rt_mutex_schedule(void);
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extern void rt_mutex_post_schedule(void);
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/*
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* Must hold either p->pi_lock or task_rq(p)->lock.
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*/
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static inline struct task_struct *rt_mutex_get_top_task(struct task_struct *p)
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{
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return p->pi_top_task;
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}
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extern void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task);
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extern void rt_mutex_adjust_pi(struct task_struct *p);
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#else
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static inline struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
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{
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return NULL;
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}
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# define rt_mutex_adjust_pi(p) do { } while (0)
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#endif
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extern void normalize_rt_tasks(void);
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/*
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* default timeslice is 100 msecs (used only for SCHED_RR tasks).
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* Timeslices get refilled after they expire.
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*/
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#define RR_TIMESLICE (100 * HZ / 1000)
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#endif /* _LINUX_SCHED_RT_H */
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