Upgrade to 4.4.50-rt62

[kvmfornfv.git] / kernel / kernel / jump_label.c

diff --git a/kernel/kernel/jump_label.c b/kernel/kernel/jump_label.c
index 05254ee..453ec42 100644 (file)
--- a/kernel/kernel/jump_label.c
+++ b/kernel/kernel/jump_label.c
@@ -58,13 +58,36 @@ static void jump_label_update(struct static_key *key);
 
 void static_key_slow_inc(struct static_key *key)
 {
+       int v, v1;
+
        STATIC_KEY_CHECK_USE();
-       if (atomic_inc_not_zero(&key->enabled))
-               return;
+
+       /*
+        * Careful if we get concurrent static_key_slow_inc() calls;
+        * later calls must wait for the first one to _finish_ the
+        * jump_label_update() process.  At the same time, however,
+        * the jump_label_update() call below wants to see
+        * static_key_enabled(&key) for jumps to be updated properly.
+        *
+        * So give a special meaning to negative key->enabled: it sends
+        * static_key_slow_inc() down the slow path, and it is non-zero
+        * so it counts as "enabled" in jump_label_update().  Note that
+        * atomic_inc_unless_negative() checks >= 0, so roll our own.
+        */
+       for (v = atomic_read(&key->enabled); v > 0; v = v1) {
+               v1 = atomic_cmpxchg(&key->enabled, v, v + 1);
+               if (likely(v1 == v))
+                       return;
+       }
 
        jump_label_lock();
-       if (atomic_inc_return(&key->enabled) == 1)
+       if (atomic_read(&key->enabled) == 0) {
+               atomic_set(&key->enabled, -1);
                jump_label_update(key);
+               atomic_set(&key->enabled, 1);
+       } else {
+               atomic_inc(&key->enabled);
+       }
        jump_label_unlock();
 }
 EXPORT_SYMBOL_GPL(static_key_slow_inc);
@@ -72,6 +95,13 @@ 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)
 {
+       /*
+        * The negative count check is valid even when a negative
+        * key->enabled is in use by static_key_slow_inc(); a
+        * __static_key_slow_dec() before the first static_key_slow_inc()
+        * returns is unbalanced, because all other static_key_slow_inc()
+        * instances block while the update is in progress.
+        */
        if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
                WARN(atomic_read(&key->enabled) < 0,
                     "jump label: negative count!\n");
@@ -108,6 +138,13 @@ void static_key_slow_dec_deferred(struct static_key_deferred *key)
 }
 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 
+void static_key_deferred_flush(struct static_key_deferred *key)
+{
+       STATIC_KEY_CHECK_USE();
+       flush_delayed_work(&key->work);
+}
+EXPORT_SYMBOL_GPL(static_key_deferred_flush);
+
 void jump_label_rate_limit(struct static_key_deferred *key,
                unsigned long rl)
 {