Commit 6991436c authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
Browse files

sched/core: Provide a scheduling point for RT locks 



RT enabled kernels substitute spin/rwlocks with 'sleeping' variants based
on rtmutexes. Blocking on such a lock is similar to preemption versus:

 - I/O scheduling and worker handling, because these functions might block
   on another substituted lock, or come from a lock contention within these
   functions.

 - RCU considers this like a preemption, because the task might be in a read
   side critical section.

Add a separate scheduling point for this, and hand a new scheduling mode
argument to __schedule() which allows, along with separate mode masks, to
handle this gracefully from within the scheduler, without proliferating that
to other subsystems like RCU.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.372319055@linutronix.de
parent b4bfa3fc

include/linux/sched.h

+3 −0
Original line number Diff line number Diff line
@@ -288,6 +288,9 @@ extern long schedule_timeout_idle(long timeout); 
asmlinkage void schedule(void);

extern void schedule_preempt_disabled(void);

asmlinkage void preempt_schedule_irq(void);

#ifdef CONFIG_PREEMPT_RT

 extern void schedule_rtlock(void);

#endif



extern int __must_check io_schedule_prepare(void);

extern void io_schedule_finish(int token);

kernel/sched/core.c

+19 −1
Original line number Diff line number Diff line
@@ -5829,7 +5829,13 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 
 */

#define SM_NONE			0x0

#define SM_PREEMPT		0x1

#define SM_RTLOCK_WAIT		0x2



#ifndef CONFIG_PREEMPT_RT

# define SM_MASK_PREEMPT	(~0U)

#else

# define SM_MASK_PREEMPT	SM_PREEMPT

#endif



/*

 * __schedule() is the main scheduler function.
@@ -6134,6 +6140,18 @@ void __sched schedule_preempt_disabled(void) 
	preempt_disable();

}



#ifdef CONFIG_PREEMPT_RT

void __sched notrace schedule_rtlock(void)

{

	do {

		preempt_disable();

		__schedule(SM_RTLOCK_WAIT);

		sched_preempt_enable_no_resched();

	} while (need_resched());

}

NOKPROBE_SYMBOL(schedule_rtlock);

#endif



static void __sched notrace preempt_schedule_common(void)

{

	do {