From 6991436c2b5d91d5358d9914ae2df22b9a1d1dc9 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 15 Aug 2021 23:27:48 +0200
Subject: [PATCH] sched/core: Provide a scheduling point for RT locks
Git-commit: 6991436c2b5d91d5358d9914ae2df22b9a1d1dc9
Patch-mainline: v5.15-rc1
References: bsc#1190137 bsc#1189998
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
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
include/linux/sched.h | 3 +++
kernel/sched/core.c | 20 +++++++++++++++++++-
2 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 02714b9a3ff9..746dfc06a35c 100644
--- 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 ebc24e136222..c89c1d45dd0b 100644
--- 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 {
--
2.26.2