Re: [PATCH] mm: slub: annotate kmem_cache_node->list_lock as raw_spinlock

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Wed, Apr 12, 2023 at 08:50:29AM +0200, Vlastimil Babka wrote:

> > --- a/lib/debugobjects.c
> > +++ b/lib/debugobjects.c
> > @@ -562,10 +562,10 @@ __debug_object_init(void *addr, const struct debug_obj_descr *descr, int onstack
> >         unsigned long flags;
> > 
> >         /*
> > -        * On RT enabled kernels the pool refill must happen in preemptible
> > +        * The pool refill must happen in preemptible
> >          * context:
> >          */
> > -       if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible())
> > +       if (preemptible())
> >                 fill_pool();
> 
> +CC Peterz
> 
> Aha so this is in fact another case where the code is written with
> actual differences between PREEMPT_RT and !PREEMPT_RT in mind, but
> CONFIG_PROVE_RAW_LOCK_NESTING always assumes PREEMPT_RT?

Ooh, tricky, yes. PROVE_RAW_LOCK_NESTING always follows the PREEMP_RT
rules and does not expect trickery like the above.

Something like the completely untested below might be of help..

---
diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
index d22430840b53..f3120d6a7d9e 100644
--- a/include/linux/lockdep_types.h
+++ b/include/linux/lockdep_types.h
@@ -33,6 +33,7 @@ enum lockdep_wait_type {
 enum lockdep_lock_type {
 	LD_LOCK_NORMAL = 0,	/* normal, catch all */
 	LD_LOCK_PERCPU,		/* percpu */
+	LD_LOCK_WAIT,		/* annotation */
 	LD_LOCK_MAX,
 };
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 50d4863974e7..a4077f5bb75b 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2279,8 +2279,9 @@ static inline bool usage_skip(struct lock_list *entry, void *mask)
 	 * As a result, we will skip local_lock(), when we search for irq
 	 * inversion bugs.
 	 */
-	if (entry->class->lock_type == LD_LOCK_PERCPU) {
-		if (DEBUG_LOCKS_WARN_ON(entry->class->wait_type_inner < LD_WAIT_CONFIG))
+	if (entry->class->lock_type != LD_LOCK_NORMAL) {
+		if (entry->class->lock_type == LD_LOCK_PERCPU &&
+		    DEBUG_LOCKS_WARN_ON(entry->class->wait_type_inner < LD_WAIT_CONFIG))
 			return false;
 
 		return true;
@@ -4752,7 +4753,8 @@ static int check_wait_context(struct task_struct *curr, struct held_lock *next)
 
 	for (; depth < curr->lockdep_depth; depth++) {
 		struct held_lock *prev = curr->held_locks + depth;
-		u8 prev_inner = hlock_class(prev)->wait_type_inner;
+		struct lock_class *class = hlock_class(prev);
+		u8 prev_inner = class->wait_type_inner;
 
 		if (prev_inner) {
 			/*
@@ -4762,6 +4764,12 @@ static int check_wait_context(struct task_struct *curr, struct held_lock *next)
 			 * Also due to trylocks.
 			 */
 			curr_inner = min(curr_inner, prev_inner);
+
+			/*
+			 * Allow override for annotations.
+			 */
+			if (unlikely(class->lock_type == LD_LOCK_WAIT))
+				curr_inner = prev_inner;
 		}
 	}
 
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index df86e649d8be..fae71ef72a16 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -565,8 +565,16 @@ __debug_object_init(void *addr, const struct debug_obj_descr *descr, int onstack
 	 * On RT enabled kernels the pool refill must happen in preemptible
 	 * context:
 	 */
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible())
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible()) {
+		static lockdep_map dep_map = {
+			.name = "wait-type-override",
+			.wait_type_inner = LD_WAIT_SLEEP,
+			.lock_type = LD_LOCK_WAIT,
+		};
+		lock_map_acquire(&dep_map);
 		fill_pool();
+		lock_map_release(&dep_map);
+	}
 
 	db = get_bucket((unsigned long) addr);