[1/3] jump_labels: fix concurrent static_key_enable/disable()
diff mbox series

Message ID 1501601046-35683-2-git-send-email-pbonzini@redhat.com
State New, archived
Headers show
Series
  • jump_labels: concurrency fixes
Related show

Commit Message

Paolo Bonzini Aug. 1, 2017, 3:24 p.m. UTC
static_key_enable/disable are trying to cap the static key count to
0/1.  However, their use of key->enabled is outside jump_label_lock
so they do not really ensure that.

Rewrite them to do a quick check for an already enabled (respectively,
already disabled), and then recheck under the jump label lock.  Unlike
static_key_slow_inc/dec, a failed check under the jump label lock does
not modify key->enabled.

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 include/linux/jump_label.h | 22 +++++++++--------
 kernel/jump_label.c        | 59 +++++++++++++++++++++++++++++-----------------
 2 files changed, 49 insertions(+), 32 deletions(-)

Comments

Peter Zijlstra Aug. 1, 2017, 4:45 p.m. UTC | #1
Thanks for doing these patches, I hadn't come around to them yet.

On Tue, Aug 01, 2017 at 05:24:04PM +0200, Paolo Bonzini wrote:
>  
> +void static_key_enable(struct static_key *key)
> +{
> +	STATIC_KEY_CHECK_USE();
> +	if (atomic_read(&key->enabled) > 0) {
> +		WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
> +		return;
> +	}
> +
> +	cpus_read_lock();
> +	jump_label_lock();
> +	if (atomic_read(&key->enabled) == 0) {
> +		atomic_set(&key->enabled, -1);
> +		jump_label_update(key);

As per the previous discussion, should I do a patch adding barriers here
(or using atomic_set_release()) such that we close the window where a
concurrent inc/enable sees 1 but not all text changes?

> +		atomic_set(&key->enabled, 1);
> +	}
> +	jump_label_unlock();
> +	cpus_read_unlock();
> +}
> +EXPORT_SYMBOL_GPL(static_key_enable);
Paolo Bonzini Aug. 1, 2017, 4:46 p.m. UTC | #2
On 01/08/2017 18:45, Peter Zijlstra wrote:
> 
> Thanks for doing these patches, I hadn't come around to them yet.
> 
> On Tue, Aug 01, 2017 at 05:24:04PM +0200, Paolo Bonzini wrote:
>>  
>> +void static_key_enable(struct static_key *key)
>> +{
>> +	STATIC_KEY_CHECK_USE();
>> +	if (atomic_read(&key->enabled) > 0) {
>> +		WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
>> +		return;
>> +	}
>> +
>> +	cpus_read_lock();
>> +	jump_label_lock();
>> +	if (atomic_read(&key->enabled) == 0) {
>> +		atomic_set(&key->enabled, -1);
>> +		jump_label_update(key);
> 
> As per the previous discussion, should I do a patch adding barriers here
> (or using atomic_set_release()) such that we close the window where a
> concurrent inc/enable sees 1 but not all text changes?

Sure, and that applies to static_key_slow_inc as well.

Paolo

>> +		atomic_set(&key->enabled, 1);
>> +	}
>> +	jump_label_unlock();
>> +	cpus_read_unlock();
>> +}
>> +EXPORT_SYMBOL_GPL(static_key_enable);

Patch
diff mbox series

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 2afd74b9d844..740a42ea7f7f 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -234,22 +234,24 @@  static inline int jump_label_apply_nops(struct module *mod)
 
 static inline void static_key_enable(struct static_key *key)
 {
-	int count = static_key_count(key);
-
-	WARN_ON_ONCE(count < 0 || count > 1);
+	STATIC_KEY_CHECK_USE();
 
-	if (!count)
-		static_key_slow_inc(key);
+	if (atomic_read(&key->enabled) != 0) {
+		WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
+		return;
+	}
+	atomic_set(&key->enabled, 1);
 }
 
 static inline void static_key_disable(struct static_key *key)
 {
-	int count = static_key_count(key);
-
-	WARN_ON_ONCE(count < 0 || count > 1);
+	STATIC_KEY_CHECK_USE();
 
-	if (count)
-		static_key_slow_dec(key);
+	if (atomic_read(&key->enabled) != 1) {
+		WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
+		return;
+	}
+	atomic_set(&key->enabled, 0);
 }
 
 #define STATIC_KEY_INIT_TRUE	{ .enabled = ATOMIC_INIT(1) }
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 6c9cb208ac48..04a574fd5844 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -78,28 +78,6 @@  int static_key_count(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_count);
 
-void static_key_enable(struct static_key *key)
-{
-	int count = static_key_count(key);
-
-	WARN_ON_ONCE(count < 0 || count > 1);
-
-	if (!count)
-		static_key_slow_inc(key);
-}
-EXPORT_SYMBOL_GPL(static_key_enable);
-
-void static_key_disable(struct static_key *key)
-{
-	int count = static_key_count(key);
-
-	WARN_ON_ONCE(count < 0 || count > 1);
-
-	if (count)
-		static_key_slow_dec(key);
-}
-EXPORT_SYMBOL_GPL(static_key_disable);
-
 void static_key_slow_inc(struct static_key *key)
 {
 	int v, v1;
@@ -136,6 +114,43 @@  void static_key_slow_inc(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_slow_inc);
 
+void static_key_enable(struct static_key *key)
+{
+	STATIC_KEY_CHECK_USE();
+	if (atomic_read(&key->enabled) > 0) {
+		WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
+		return;
+	}
+
+	cpus_read_lock();
+	jump_label_lock();
+	if (atomic_read(&key->enabled) == 0) {
+		atomic_set(&key->enabled, -1);
+		jump_label_update(key);
+		atomic_set(&key->enabled, 1);
+	}
+	jump_label_unlock();
+	cpus_read_unlock();
+}
+EXPORT_SYMBOL_GPL(static_key_enable);
+
+void static_key_disable(struct static_key *key)
+{
+	STATIC_KEY_CHECK_USE();
+	if (atomic_read(&key->enabled) != 1) {
+		WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
+		return;
+	}
+
+	cpus_read_lock();
+	jump_label_lock();
+	if (atomic_cmpxchg(&key->enabled, 1, 0))
+		jump_label_update(key);
+	jump_label_unlock();
+	cpus_read_unlock();
+}
+EXPORT_SYMBOL_GPL(static_key_disable);
+
 static void __static_key_slow_dec(struct static_key *key,
 		unsigned long rate_limit, struct delayed_work *work)
 {