cpuset: add a missing unlock in cpuset_write_resmask()

Don't forget to release cgroup_mutex if alloc_trial_cpuset() fails.

[akpm@linux-foundation.org: avoid multiple return points]
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/cpuset.c

@@ -1575,8 +1575,10 @@ static int cpuset_write_resmask(struct cgroup *cgrp, struct cftype *cft,
 		return -ENODEV;
 
 	trialcs = alloc_trial_cpuset(cs);
-	if (!trialcs)
-		return -ENOMEM;
+	if (!trialcs) {
+		retval = -ENOMEM;
+		goto out;
+	}
 
 	switch (cft->private) {
 	case FILE_CPULIST:
@@ -1591,6 +1593,7 @@ static int cpuset_write_resmask(struct cgroup *cgrp, struct cftype *cft,
 	}
 
 	free_trial_cpuset(trialcs);
+out:
 	cgroup_unlock();
 	return retval;
 }