linux-kernel - Re: [PATCH 1/4] locking/lockdep: Use hashtable.h for lock_keys

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Message-ID: <68111ac5.810a0220.2b20a.1d32@mx.google.com>
Date: Tue, 29 Apr 2025 11:30:26 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Sasha Levin <sashal@...nel.org>
Cc: peterz@...radead.org, mingo@...hat.com, will@...nel.org,
	longman@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] locking/lockdep: Use hashtable.h for lock_keys_hash

Hi Sasha,

Thanks for the patches. I want to let you know that we are currently
doing some changes on the hashlist usage in lockdep:

	https://lore.kernel.org/lkml/20250414060055.341516-1-boqun.feng@gmail.com/	

so, it may take a while for me to back looking into this (until that get
sorted).

Regards,
Boqun

On Thu, Mar 20, 2025 at 10:31:17AM -0400, Sasha Levin wrote:
> Convert the lock_keys_hash array in lockdep.c to use the generic
> hashtable implementation from hashtable.h instead of the manual
> hlist_head array implementation.
> 
> This simplifies the code and makes it more maintainable by using the
> standard hashtable API defined in hashtable.h, while preserving the
> RCU-safe behavior with proper RCU variants of the hashtable functions.
> 
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  kernel/locking/lockdep.c | 34 ++++++++++++++++------------------
>  1 file changed, 16 insertions(+), 18 deletions(-)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 4470680f02269..160cf8310eda0 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -57,6 +57,7 @@
>  #include <linux/lockdep.h>
>  #include <linux/context_tracking.h>
>  #include <linux/console.h>
> +#include <linux/hashtable.h>
>  
>  #include <asm/sections.h>
>  
> @@ -212,8 +213,7 @@ static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);
>   * in use.
>   */
>  #define KEYHASH_BITS		(MAX_LOCKDEP_KEYS_BITS - 1)
> -#define KEYHASH_SIZE		(1UL << KEYHASH_BITS)
> -static struct hlist_head lock_keys_hash[KEYHASH_SIZE];
> +static DEFINE_HASHTABLE(lock_keys_hash, KEYHASH_BITS);
>  unsigned long nr_lock_classes;
>  unsigned long nr_zapped_classes;
>  unsigned long max_lock_class_idx;
> @@ -1209,32 +1209,28 @@ static void init_data_structures_once(void)
>  	init_chain_block_buckets();
>  }
>  
> -static inline struct hlist_head *keyhashentry(const struct lock_class_key *key)
> -{
> -	unsigned long hash = hash_long((uintptr_t)key, KEYHASH_BITS);
> -
> -	return lock_keys_hash + hash;
> -}
>  
>  /* Register a dynamically allocated key. */
>  void lockdep_register_key(struct lock_class_key *key)
>  {
> -	struct hlist_head *hash_head;
>  	struct lock_class_key *k;
> +	unsigned long hash;
>  	unsigned long flags;
>  
>  	if (WARN_ON_ONCE(static_obj(key)))
>  		return;
> -	hash_head = keyhashentry(key);
> +
> +	hash = hash_long((uintptr_t)key, KEYHASH_BITS);
>  
>  	raw_local_irq_save(flags);
>  	if (!graph_lock())
>  		goto restore_irqs;
> -	hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
> +
> +	hash_for_each_possible_rcu(lock_keys_hash, k, hash_entry, hash) {
>  		if (WARN_ON_ONCE(k == key))
>  			goto out_unlock;
>  	}
> -	hlist_add_head_rcu(&key->hash_entry, hash_head);
> +	hash_add_rcu(lock_keys_hash, &key->hash_entry, hash);
>  out_unlock:
>  	graph_unlock();
>  restore_irqs:
> @@ -1245,8 +1241,8 @@ EXPORT_SYMBOL_GPL(lockdep_register_key);
>  /* Check whether a key has been registered as a dynamic key. */
>  static bool is_dynamic_key(const struct lock_class_key *key)
>  {
> -	struct hlist_head *hash_head;
>  	struct lock_class_key *k;
> +	unsigned long hash;
>  	bool found = false;
>  
>  	if (WARN_ON_ONCE(static_obj(key)))
> @@ -1260,10 +1256,10 @@ static bool is_dynamic_key(const struct lock_class_key *key)
>  	if (!debug_locks)
>  		return true;
>  
> -	hash_head = keyhashentry(key);
> +	hash = hash_long((uintptr_t)key, KEYHASH_BITS);
>  
>  	rcu_read_lock();
> -	hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
> +	hash_for_each_possible_rcu(lock_keys_hash, k, hash_entry, hash) {
>  		if (k == key) {
>  			found = true;
>  			break;
> @@ -6561,9 +6557,9 @@ void lockdep_reset_lock(struct lockdep_map *lock)
>   */
>  void lockdep_unregister_key(struct lock_class_key *key)
>  {
> -	struct hlist_head *hash_head = keyhashentry(key);
>  	struct lock_class_key *k;
>  	struct pending_free *pf;
> +	unsigned long hash;
>  	unsigned long flags;
>  	bool found = false;
>  	bool need_callback = false;
> @@ -6573,12 +6569,14 @@ void lockdep_unregister_key(struct lock_class_key *key)
>  	if (WARN_ON_ONCE(static_obj(key)))
>  		return;
>  
> +	hash = hash_long((uintptr_t)key, KEYHASH_BITS);
> +
>  	raw_local_irq_save(flags);
>  	lockdep_lock();
>  
> -	hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
> +	hash_for_each_possible(lock_keys_hash, k, hash_entry, hash) {
>  		if (k == key) {
> -			hlist_del_rcu(&k->hash_entry);
> +			hash_del_rcu(&k->hash_entry);
>  			found = true;
>  			break;
>  		}
> -- 
> 2.39.5
>