cpuset: re-structure update_cpumask() a bit

Check if cpus_allowed is to be changed before calling validate_change().

This won't change any behavior, but later it will allow us to do this:

 # mkdir /cpuset/child
 # echo $$ > /cpuset/child/tasks	/* empty cpuset */
 # echo > /cpuset/child/cpuset.cpus	/* do nothing, won't fail */

Without this patch, the last operation will fail.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 51f8e1d5a2a9..535dce685eec 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -856,14 +856,15 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
                 if (!cpumask_subset(trialcs->cpus_allowed, cpu_active_mask))
                         return -EINVAL;
         }
-        retval = validate_change(cs, trialcs);
-        if (retval < 0)
-                return retval;
 
         /* Nothing to do if the cpus didn't change */
         if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
                 return 0;
 
+        retval = validate_change(cs, trialcs);
+        if (retval < 0)
+                return retval;
+
         retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
         if (retval)
                 return retval;