rfkill: sync before userspace visibility/changes

If userspace quickly opens /dev/rfkill after a new
instance was created, it might see the old state of
the instance from before the sync work runs and may
even _change_ the state, only to have the sync work
change it again.

Fix this by doing the sync inline where needed, not
just for /dev/rfkill but also for sysfs.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/rfkill/core.c

@@ -48,6 +48,7 @@ struct rfkill {
 	bool			persistent;
 	bool			polling_paused;
 	bool			suspended;
+	bool			need_sync;
 
 	const struct rfkill_ops	*ops;
 	void			*data;
@@ -368,6 +369,17 @@ static void rfkill_set_block(struct rfkill *rfkill, bool blocked)
 		rfkill_event(rfkill);
 }
 
+static void rfkill_sync(struct rfkill *rfkill)
+{
+	lockdep_assert_held(&rfkill_global_mutex);
+
+	if (!rfkill->need_sync)
+		return;
+
+	rfkill_set_block(rfkill, rfkill_global_states[rfkill->type].cur);
+	rfkill->need_sync = false;
+}
+
 static void rfkill_update_global_state(enum rfkill_type type, bool blocked)
 {
 	int i;
@@ -730,6 +742,10 @@ static ssize_t soft_show(struct device *dev, struct device_attribute *attr,
 {
 	struct rfkill *rfkill = to_rfkill(dev);
 
+	mutex_lock(&rfkill_global_mutex);
+	rfkill_sync(rfkill);
+	mutex_unlock(&rfkill_global_mutex);
+
 	return sysfs_emit(buf, "%d\n", (rfkill->state & RFKILL_BLOCK_SW) ? 1 : 0);
 }
 
@@ -751,6 +767,7 @@ static ssize_t soft_store(struct device *dev, struct device_attribute *attr,
 		return -EINVAL;
 
 	mutex_lock(&rfkill_global_mutex);
+	rfkill_sync(rfkill);
 	rfkill_set_block(rfkill, state);
 	mutex_unlock(&rfkill_global_mutex);
 
@@ -783,6 +800,10 @@ static ssize_t state_show(struct device *dev, struct device_attribute *attr,
 {
 	struct rfkill *rfkill = to_rfkill(dev);
 
+	mutex_lock(&rfkill_global_mutex);
+	rfkill_sync(rfkill);
+	mutex_unlock(&rfkill_global_mutex);
+
 	return sysfs_emit(buf, "%d\n", user_state_from_blocked(rfkill->state));
 }
 
@@ -805,6 +826,7 @@ static ssize_t state_store(struct device *dev, struct device_attribute *attr,
 		return -EINVAL;
 
 	mutex_lock(&rfkill_global_mutex);
+	rfkill_sync(rfkill);
 	rfkill_set_block(rfkill, state == RFKILL_USER_STATE_SOFT_BLOCKED);
 	mutex_unlock(&rfkill_global_mutex);
 
@@ -1032,14 +1054,10 @@ static void rfkill_uevent_work(struct work_struct *work)
 
 static void rfkill_sync_work(struct work_struct *work)
 {
-	struct rfkill *rfkill;
-	bool cur;
-
-	rfkill = container_of(work, struct rfkill, sync_work);
+	struct rfkill *rfkill = container_of(work, struct rfkill, sync_work);
 
 	mutex_lock(&rfkill_global_mutex);
-	cur = rfkill_global_states[rfkill->type].cur;
-	rfkill_set_block(rfkill, cur);
+	rfkill_sync(rfkill);
 	mutex_unlock(&rfkill_global_mutex);
 }
 
@@ -1087,6 +1105,7 @@ int __must_check rfkill_register(struct rfkill *rfkill)
 			round_jiffies_relative(POLL_INTERVAL));
 
 	if (!rfkill->persistent || rfkill_epo_lock_active) {
+		rfkill->need_sync = true;
 		schedule_work(&rfkill->sync_work);
 	} else {
 #ifdef CONFIG_RFKILL_INPUT
@@ -1171,6 +1190,7 @@ static int rfkill_fop_open(struct inode *inode, struct file *file)
 		ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 		if (!ev)
 			goto free;
+		rfkill_sync(rfkill);
 		rfkill_fill_event(&ev->ev, rfkill, RFKILL_OP_ADD);
 		list_add_tail(&ev->list, &data->events);
 	}