sched: Enable context analysis for core.c and fair.c

This demonstrates a larger conversion to use Clang's context
analysis. The benefit is additional static checking of locking rules,
along with better documentation.

Notably, kernel/sched contains sufficiently complex synchronization
patterns, and application to core.c & fair.c demonstrates that the
latest Clang version has become powerful enough to start applying this
to more complex subsystems (with some modest annotations and changes).

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-37-elver@google.com

4 files changed, 14 insertions, 5 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d395f2810fac..c4022647282e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2094,9 +2094,9 @@ static inline int _cond_resched(void)
 	_cond_resched();			\
 })
 
-extern int __cond_resched_lock(spinlock_t *lock);
-extern int __cond_resched_rwlock_read(rwlock_t *lock);
-extern int __cond_resched_rwlock_write(rwlock_t *lock);
+extern int __cond_resched_lock(spinlock_t *lock) __must_hold(lock);
+extern int __cond_resched_rwlock_read(rwlock_t *lock) __must_hold_shared(lock);
+extern int __cond_resched_rwlock_write(rwlock_t *lock) __must_hold(lock);
 
 #define MIGHT_RESCHED_RCU_SHIFT		8
 #define MIGHT_RESCHED_PREEMPT_MASK	((1U << MIGHT_RESCHED_RCU_SHIFT) - 1)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index a63f65aa5bdd..a22248aebcf9 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -738,10 +738,12 @@ static inline int thread_group_empty(struct task_struct *p)
 		(thread_group_leader(p) && !thread_group_empty(p))
 
 extern struct sighand_struct *lock_task_sighand(struct task_struct *task,
-						unsigned long *flags);
+						unsigned long *flags)
+	__acquires(&task->sighand->siglock);
 
 static inline void unlock_task_sighand(struct task_struct *task,
 						unsigned long *flags)
+	__releases(&task->sighand->siglock)
 {
 	spin_unlock_irqrestore(&task->sighand->siglock, *flags);
 }
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 525aa2a632b2..41ed884cffc9 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -214,15 +214,19 @@ static inline struct vm_struct *task_stack_vm_area(const struct task_struct *t)
  * write_lock_irq(&tasklist_lock), neither inside nor outside.
  */
 static inline void task_lock(struct task_struct *p)
+	__acquires(&p->alloc_lock)
 {
 	spin_lock(&p->alloc_lock);
 }
 
 static inline void task_unlock(struct task_struct *p)
+	__releases(&p->alloc_lock)
 {
 	spin_unlock(&p->alloc_lock);
 }
 
-DEFINE_GUARD(task_lock, struct task_struct *, task_lock(_T), task_unlock(_T))
+DEFINE_LOCK_GUARD_1(task_lock, struct task_struct, task_lock(_T->lock), task_unlock(_T->lock))
+DECLARE_LOCK_GUARD_1_ATTRS(task_lock, __acquires(&_T->alloc_lock), __releases(&(*(struct task_struct **)_T)->alloc_lock))
+#define class_task_lock_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(task_lock, _T)
 
 #endif /* _LINUX_SCHED_TASK_H */
diff --git a/include/linux/sched/wake_q.h b/include/linux/sched/wake_q.h
index 0f28b4623ad4..765bbc3d54be 100644
--- a/include/linux/sched/wake_q.h
+++ b/include/linux/sched/wake_q.h
@@ -66,6 +66,7 @@ extern void wake_up_q(struct wake_q_head *head);
 /* Spin unlock helpers to unlock and call wake_up_q with preempt disabled */
 static inline
 void raw_spin_unlock_wake(raw_spinlock_t *lock, struct wake_q_head *wake_q)
+	__releases(lock)
 {
 	guard(preempt)();
 	raw_spin_unlock(lock);
@@ -77,6 +78,7 @@ void raw_spin_unlock_wake(raw_spinlock_t *lock, struct wake_q_head *wake_q)
 
 static inline
 void raw_spin_unlock_irq_wake(raw_spinlock_t *lock, struct wake_q_head *wake_q)
+	__releases(lock)
 {
 	guard(preempt)();
 	raw_spin_unlock_irq(lock);
@@ -89,6 +91,7 @@ void raw_spin_unlock_irq_wake(raw_spinlock_t *lock, struct wake_q_head *wake_q)
 static inline
 void raw_spin_unlock_irqrestore_wake(raw_spinlock_t *lock, unsigned long flags,
 				     struct wake_q_head *wake_q)
+	__releases(lock)
 {
 	guard(preempt)();
 	raw_spin_unlock_irqrestore(lock, flags);