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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.372319055@linutronix.de

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 02714b9..746dfc0 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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);

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ebc24e1..c89c1d4 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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_MASK_PREEMPT                (~0U)
+#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 {