sched: convert sys_sched_getaffinity() to cpumask_var_t.

Impact: stack usage reduction

Dynamically allocating cpumasks (when CONFIG_CPUMASK_OFFSTACK) saves
space in the stack.  cpumask_var_t is just a struct cpumask for
!CONFIG_CPUMASK_OFFSTACK.

Some jiggling here to make sure we always exit at the bottom (so we hit
the free_cpumask_var there).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 13 insertions, 8 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 67383e7f1ccd..6deff24349b6 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5499,19 +5499,24 @@ asmlinkage long sys_sched_getaffinity(pid_t pid, unsigned int len,
                                       unsigned long __user *user_mask_ptr)
 {
         int ret;
-        cpumask_t mask;
+        cpumask_var_t mask;
 
-        if (len < sizeof(cpumask_t))
+        if (len < cpumask_size())
                 return -EINVAL;
 
-        ret = sched_getaffinity(pid, &mask);
-        if (ret < 0)
-                return ret;
+        if (!alloc_cpumask_var(&mask, GFP_KERNEL))
+                return -ENOMEM;
 
-        if (copy_to_user(user_mask_ptr, &mask, sizeof(cpumask_t)))
-                return -EFAULT;
+        ret = sched_getaffinity(pid, mask);
+        if (ret == 0) {
+                if (copy_to_user(user_mask_ptr, mask, cpumask_size()))
+                        ret = -EFAULT;
+                else
+                        ret = cpumask_size();
+        }
+        free_cpumask_var(mask);
 
-        return sizeof(cpumask_t);
+        return ret;
 }
 
 /**