[RFC PATCH 05/28] sched: Add cond_resched_rwlock

[Ben Gardon <bgardon@google.com>]

Rescheduling while holding a spin lock is essential for keeping long
running kernel operations running smoothly. Add the facility to
cond_resched read/write spin locks.

RFC_NOTE: The current implementation of this patch set uses a read/write
lock to replace the existing MMU spin lock. See the next patch in this
series for more on why a read/write lock was chosen, and possible
alternatives.

Signed-off-by: Ben Gardon <bgardon@google.com>
---
 include/linux/sched.h | 11 +++++++++++
 kernel/sched/core.c   | 23 +++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 70db597d6fd4f..4d1fd96693d9b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1767,12 +1767,23 @@ static inline int _cond_resched(void) { return 0; }
 })
 
 extern int __cond_resched_lock(spinlock_t *lock);
+extern int __cond_resched_rwlock(rwlock_t *lock, bool write_lock);
 
 #define cond_resched_lock(lock) ({				\
 	___might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);\
 	__cond_resched_lock(lock);				\
 })
 
+#define cond_resched_rwlock_read(lock) ({			\
+	__might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);	\
+	__cond_resched_rwlock(lock, false);			\
+})
+
+#define cond_resched_rwlock_write(lock) ({			\
+	__might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);	\
+	__cond_resched_rwlock(lock, true);			\
+})
+
 static inline void cond_resched_rcu(void)
 {
 #if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_PREEMPT_RCU)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f9a1346a5fa95..ba7ed4bed5036 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5663,6 +5663,29 @@ int __cond_resched_lock(spinlock_t *lock)
 }
 EXPORT_SYMBOL(__cond_resched_lock);
 
+int __cond_resched_rwlock(rwlock_t *lock, bool write_lock)
+{
+	int ret = 0;
+
+	lockdep_assert_held(lock);
+	if (should_resched(PREEMPT_LOCK_OFFSET)) {
+		if (write_lock) {
+			write_unlock(lock);
+			preempt_schedule_common();
+			write_lock(lock);
+		} else {
+			read_unlock(lock);
+			preempt_schedule_common();
+			read_lock(lock);
+		}
+
+		ret = 1;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(__cond_resched_rwlock);
+
 /**
  * yield - yield the current processor to other threads.
  *
-- 
2.23.0.444.g18eeb5a265-goog