linux-kernel - [patch 1/8] sched: Clean up the might

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Message-ID: <20210923165357.928693482@linutronix.de>
Date:   Thu, 23 Sep 2021 18:54:35 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Sebastian Siewior <bigeasy@...utronix.de>
Subject: [patch 1/8] sched: Clean up the might_sleep() underscore zoo

__might_sleep() vs. ___might_sleep() is hard to distinguish. Aside of that
the three underscore variant is exposed to provide a checkpoint for
rescheduling points which are distinct from blocking points.

They are semantically a preemption point which means that scheduling is
state preserving. A real blocking operation, e.g. mutex_lock(), wait*(),
which cannot preserve a task state which is not equal to RUNNING.

While technically blocking on a "sleeping" spinlock in RT enabled kernels
falls into the voluntary scheduling category because it has to wait until
the contended spin/rw lock becomes available, the RT lock substitution code
can semantically be mapped to a voluntary preemption because the RT lock
substitution code and the scheduler are providing mechanisms to preserve
the task state and to take regular non-lock related wakeups into account.

Rename ___might_sleep() to __might_resched() to make the distinction of
these functions clear.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 include/linux/kernel.h       |    6 +++---
 include/linux/sched.h        |    8 ++++----
 kernel/locking/spinlock_rt.c |    6 +++---
 kernel/sched/core.c          |    6 +++---
 4 files changed, 13 insertions(+), 13 deletions(-)

--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -111,7 +111,7 @@ static __always_inline void might_resche
 #endif /* CONFIG_PREEMPT_* */
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
-extern void ___might_sleep(const char *file, int line, int preempt_offset);
+extern void __might_resched(const char *file, int line, int preempt_offset);
 extern void __might_sleep(const char *file, int line, int preempt_offset);
 extern void __cant_sleep(const char *file, int line, int preempt_offset);
 extern void __cant_migrate(const char *file, int line);
@@ -168,8 +168,8 @@ extern void __cant_migrate(const char *f
  */
 # define non_block_end() WARN_ON(current->non_block_count-- == 0)
 #else
-  static inline void ___might_sleep(const char *file, int line,
-				   int preempt_offset) { }
+  static inline void __might_resched(const char *file, int line,
+				     int preempt_offset) { }
   static inline void __might_sleep(const char *file, int line,
 				   int preempt_offset) { }
 # define might_sleep() do { might_resched(); } while (0)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2041,7 +2041,7 @@ static inline int _cond_resched(void) {
 #endif /* !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) */
 
 #define cond_resched() ({			\
-	___might_sleep(__FILE__, __LINE__, 0);	\
+	__might_resched(__FILE__, __LINE__, 0);	\
 	_cond_resched();			\
 })
 
@@ -2049,9 +2049,9 @@ extern int __cond_resched_lock(spinlock_
 extern int __cond_resched_rwlock_read(rwlock_t *lock);
 extern int __cond_resched_rwlock_write(rwlock_t *lock);
 
-#define cond_resched_lock(lock) ({				\
-	___might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);\
-	__cond_resched_lock(lock);				\
+#define cond_resched_lock(lock) ({					\
+	__might_resched(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);	\
+	__cond_resched_lock(lock);					\
 })
 
 #define cond_resched_rwlock_read(lock) ({			\
--- a/kernel/locking/spinlock_rt.c
+++ b/kernel/locking/spinlock_rt.c
@@ -32,7 +32,7 @@ static __always_inline void rtlock_lock(
 
 static __always_inline void __rt_spin_lock(spinlock_t *lock)
 {
-	___might_sleep(__FILE__, __LINE__, 0);
+	__might_resched(__FILE__, __LINE__, 0);
 	rtlock_lock(&lock->lock);
 	rcu_read_lock();
 	migrate_disable();
@@ -210,7 +210,7 @@ EXPORT_SYMBOL(rt_write_trylock);
 
 void __sched rt_read_lock(rwlock_t *rwlock)
 {
-	___might_sleep(__FILE__, __LINE__, 0);
+	__might_resched(__FILE__, __LINE__, 0);
 	rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_);
 	rwbase_read_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
 	rcu_read_lock();
@@ -220,7 +220,7 @@ EXPORT_SYMBOL(rt_read_lock);
 
 void __sched rt_write_lock(rwlock_t *rwlock)
 {
-	___might_sleep(__FILE__, __LINE__, 0);
+	__might_resched(__FILE__, __LINE__, 0);
 	rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_);
 	rwbase_write_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
 	rcu_read_lock();
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9446,11 +9446,11 @@ void __might_sleep(const char *file, int
 			(void *)current->task_state_change,
 			(void *)current->task_state_change);
 
-	___might_sleep(file, line, preempt_offset);
+	__might_resched(file, line, preempt_offset);
 }
 EXPORT_SYMBOL(__might_sleep);
 
-void ___might_sleep(const char *file, int line, int preempt_offset)
+void __might_resched(const char *file, int line, int preempt_offset)
 {
 	/* Ratelimiting timestamp: */
 	static unsigned long prev_jiffy;
@@ -9495,7 +9495,7 @@ void ___might_sleep(const char *file, in
 	dump_stack();
 	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 }
-EXPORT_SYMBOL(___might_sleep);
+EXPORT_SYMBOL(__might_resched);
 
 void __cant_sleep(const char *file, int line, int preempt_offset)
 {