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>

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 51f8e1d..535dce6 100644 (file)
--- 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;