Re: 回复： Re: [PATCH] bpf: disable lockdep while running BPF on lock_release

On Wed, 05 Aug 2026, NeilBrown wrote:
> 
> One thing I didn't like about the original patch is that it seemed to add
> a lot of noise to the code, passing keys around in multiple places.
> Maybe the cleanest approach would be to embed the keys in the "struct
> rhashtable" so each table gets its own key.
> Then use lockdep_register_key() in rhashtable_init and use it as needed.
> 
> You could even have just one key and use the different subclasses for
> the different locks.
>  0 for rhashtable.mutex
>  1 for rhashtable.lock
>  2 for the bit locks
> 
> but maybe that is needless complexity.
> 

So I thought about this some more and came up with this approach which
might be a good compromise.  I builds but I haven't tested it.
What do you thing?

NeilBrown

diff --git a/include/linux/rhashtable-types.h b/include/linux/rhashtable-types.h
index 57c11ec9dc64..2029fba216a8 100644
--- a/include/linux/rhashtable-types.h
+++ b/include/linux/rhashtable-types.h
@@ -97,6 +97,9 @@ struct rhashtable {
 #ifdef CONFIG_MEM_ALLOC_PROFILING
 	struct alloc_tag		*alloc_tag;
 #endif
+#ifdef CONFIG_LOCKDEP
+o	struct lock_class_key		*lockdep_key;
+#endif
 };
 
 /**
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 79f83b6eec27..f8358d43691b 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -320,18 +320,6 @@ static inline struct rhash_lock_head __rcu **rht_bucket_insert(
  * When we write to a bucket without unlocking, we use rht_assign_locked().
  */
 
-static inline unsigned long rht_lock(struct bucket_table *tbl,
-				     struct rhash_lock_head __rcu **bkt)
-	__acquires(__bitlock(0, bkt))
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	bit_spin_lock(0, (unsigned long *)bkt);
-	lock_map_acquire(&tbl->dep_map);
-	return flags;
-}
-
 static inline unsigned long rht_lock_nested(struct bucket_table *tbl,
 					struct rhash_lock_head __rcu **bucket,
 					unsigned int subclass)
@@ -341,10 +329,18 @@ static inline unsigned long rht_lock_nested(struct bucket_table *tbl,
 
 	local_irq_save(flags);
 	bit_spin_lock(0, (unsigned long *)bucket);
-	lock_acquire_exclusive(&tbl->dep_map, subclass, 0, NULL, _THIS_IP_);
+	/* subclass 0 is used for ->lock and 1 for ->mutex. 2+ for bitlocks */
+	lock_acquire_exclusive(&tbl->dep_map, subclass+2, 0, NULL, _THIS_IP_);
 	return flags;
 }
 
+static inline unsigned long rht_lock(struct bucket_table *tbl,
+				     struct rhash_lock_head __rcu **bkt)
+	__acquires(__bitlock(0, bkt))
+{
+	return rht_lock_nested(tbl, bkt, 0);
+}
+
 static inline void rht_unlock(struct bucket_table *tbl,
 			      struct rhash_lock_head __rcu **bkt,
 			      unsigned long flags)
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index d459bef245f4..17340433d983 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -189,7 +189,6 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 	struct bucket_table *tbl = NULL;
 	size_t size;
 	int i;
-	static struct lock_class_key __key;
 
 	tbl = alloc_hooks_tag(ht->alloc_tag,
 			kvmalloc_node_align_noprof(struct_size(tbl, buckets, nbuckets),
@@ -205,7 +204,10 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 	if (tbl == NULL)
 		return NULL;
 
-	lockdep_init_map(&tbl->dep_map, "rhashtable_bucket", &__key, 0);
+#ifdef CONFIG_LOCKDEP
+	/* bitlocks must use nesting level 2 or more */
+	lockdep_init_map(&tbl->dep_map, "rhashtable_bucket", ht->lockdep_key, 0);
+#endif
 
 	tbl->size = size;
 
@@ -428,7 +430,7 @@ static void rht_deferred_worker(struct work_struct *work)
 	int err = 0;
 
 	ht = container_of(work, struct rhashtable, run_work);
-	mutex_lock(&ht->mutex);
+	mutex_lock_nested(&ht->mutex, 1);
 
 	tbl = rht_dereference(ht->tbl, ht);
 	tbl = rhashtable_last_table(ht, tbl);
@@ -1172,8 +1174,14 @@ int __rhashtable_init_noprof(struct rhashtable *ht,
 		return -EINVAL;
 
 	memset(ht, 0, sizeof(*ht));
+	/* mutex_lock must use nesting level 1 */
 	mutex_init_with_key(&ht->mutex, key);
 	spin_lock_init(&ht->lock);
+	/* spin_lock can use nesting level 0 */
+	lockdep_set_class(&ht->lock, key);
+#ifdef CONFIG_LOCKDEP
+	ht->lockdep_key = key;
+#endif
 	memcpy(&ht->p, params, sizeof(*params));
 
 	alloc_tag_record(ht->alloc_tag);