[tip:smp/urgent] cpu/hotplug: Drop the device lock on error

[tip-bot for Sebastian Andrzej Siewior <tipbot@zytor.com>]

Commit-ID:  40da1b11f01e43aad1aa6cea64681b6125e8a2a7
Gitweb:     http://git.kernel.org/tip/40da1b11f01e43aad1aa6cea64681b6125e8a2a7
Author:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Fri, 2 Jun 2017 16:27:14 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 3 Jun 2017 09:35:04 +0200

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

---
 kernel/cpu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 9ae6fbe..cb51034 100644
--- 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;
 }