Re: [PATCH v3 2/2] decrement static keys on real destroy time

[Glauber Costa <glommer@parallels.com>]

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> No, what I mean is that why can't you do about the same mutexed
> activated inside static_key API function instead of requiring every
> user to worry about the function returning asynchronously.
> ie. synchronize inside static_key API instead of in the callers.
>

Like this?



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diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 4304919..f7cdc18 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -57,10 +57,11 @@ static void jump_label_update(struct static_key *key, int enable);
 
 void static_key_slow_inc(struct static_key *key)
 {
+	jump_label_lock();
+
 	if (atomic_inc_not_zero(&key->enabled))
-		return;
+		goto out;
 
-	jump_label_lock();
 	if (atomic_read(&key->enabled) == 0) {
 		if (!jump_label_get_branch_default(key))
 			jump_label_update(key, JUMP_LABEL_ENABLE);
@@ -68,6 +69,7 @@ void static_key_slow_inc(struct static_key *key)
 			jump_label_update(key, JUMP_LABEL_DISABLE);
 	}
 	atomic_inc(&key->enabled);
+out:
 	jump_label_unlock();
 }
 EXPORT_SYMBOL_GPL(static_key_slow_inc);
@@ -75,10 +77,11 @@ EXPORT_SYMBOL_GPL(static_key_slow_inc);
 static void __static_key_slow_dec(struct static_key *key,
 		unsigned long rate_limit, struct delayed_work *work)
 {
-	if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
+	jump_label_lock();
+	if (atomic_dec_and_test(&key->enabled)) {
 		WARN(atomic_read(&key->enabled) < 0,
 		     "jump label: negative count!\n");
-		return;
+		goto out;
 	}
 
 	if (rate_limit) {
@@ -90,6 +93,8 @@ static void __static_key_slow_dec(struct static_key *key,
 		else
 			jump_label_update(key, JUMP_LABEL_ENABLE);
 	}
+
+out:
 	jump_label_unlock();
 }