cpu/hotplug: Drop the device lock on error

If a custom CPU target is specified and that one is not available _or_
can't be interrupted then the code returns to userland without dropping a
lock as notices 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")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20170602142714.3ogo25f2wbq6fjpj@linutronix.de

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 9ae6fbe5b5cf5d70d5869e8efb00c61f47cf66d4..cb5103413bd8df5056b3eda682a8d93b08656dd8 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1658,13 +1658,13 @@ 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;
 }