[PATCH] cpu/hotplug: drop the device lock on error

[Sebastian Andrzej Siewior]

If a custom CPU target is specified and that one is not available _or_
can't be interrupted then leave to userland without dropping a lock as
notice by lockdep:
|echo 133 > /sys/devices/system/cpu/cpu7/hotplug/target
| ================================================
| [ BUG: lock held when returning to user space! ]
| ------------------------------------------------
| bash/503 is leaving the kernel with locks still held!
| 1 lock held by bash/503:
|  #0:  (device_hotplug_lock){+.+...}, at: [<ffffffff815b5650>] lock_device_hotplug_sysfs+0x10/0x40

So release the lock then.

Fixes: 757c989b9994 ("cpu/hotplug: Make target state writeable")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 kernel/cpu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 7435ffc6163b..912621eb2286 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1627,13 +1627,13 @@ static ssize_t write_cpuhp_target(struct device *dev,
 	ret = !sp->name || sp->cant_stop ? -EINVAL : 0;
 	mutex_unlock(&cpuhp_state_mutex);
 	if (ret)
-		return ret;
+		goto out;
 
 	if (st->state < target)
 		ret = do_cpu_up(dev->id, target);
 	else
 		ret = do_cpu_down(dev->id, target);
-
+out:
 	unlock_device_hotplug();
 	return ret ? ret : count;
 }
-- 
2.11.0