mempolicy: sanitize the usage of get_task_policy()

Cleanup + preparation. Every user of get_task_policy() calls it
unconditionally, even if it is not going to use the result.

get_task_policy() is cheap but still this does not look clean, plus
the code looks simpler if get_task_policy() is called only when this
is really needed.

Note: I hope this is correct, but it is not clear why vma_policy_mof()
doesn't fall back to get_task_policy() if ->get_policy() returns NULL.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 11 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 656db97584f0..b86b08e77b8d 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1621,14 +1621,11 @@ COMPAT_SYSCALL_DEFINE6(mbind, compat_ulong_t, start, compat_ulong_t, len,
 struct mempolicy *get_vma_policy(struct task_struct *task,
                 struct vm_area_struct *vma, unsigned long addr)
 {
-        struct mempolicy *pol = get_task_policy(task);
+        struct mempolicy *pol = NULL;
 
         if (vma) {
                 if (vma->vm_ops && vma->vm_ops->get_policy) {
-                        struct mempolicy *vpol = vma->vm_ops->get_policy(vma,
-                                                                        addr);
-                        if (vpol)
-                                pol = vpol;
+                        pol = vma->vm_ops->get_policy(vma, addr);
                 } else if (vma->vm_policy) {
                         pol = vma->vm_policy;
 
@@ -1643,12 +1640,15 @@ struct mempolicy *get_vma_policy(struct task_struct *task,
                 }
         }
 
+        if (!pol)
+                pol = get_task_policy(task);
+
         return pol;
 }
 
 bool vma_policy_mof(struct task_struct *task, struct vm_area_struct *vma)
 {
-        struct mempolicy *pol = get_task_policy(task);
+        struct mempolicy *pol = NULL;
 
         if (vma) {
                 if (vma->vm_ops && vma->vm_ops->get_policy) {
@@ -1660,11 +1660,14 @@ bool vma_policy_mof(struct task_struct *task, struct vm_area_struct *vma)
                         mpol_cond_put(pol);
 
                         return ret;
-                } else if (vma->vm_policy) {
-                        pol = vma->vm_policy;
                 }
+
+                pol = vma->vm_policy;
         }
 
+        if (!pol)
+                pol = get_task_policy(task);
+
         return pol->flags & MPOL_F_MOF;
 }
 
@@ -2068,12 +2071,12 @@ retry_cpuset:
  */
 struct page *alloc_pages_current(gfp_t gfp, unsigned order)
 {
-        struct mempolicy *pol = get_task_policy(current);
+        struct mempolicy *pol = &default_policy;
         struct page *page;
         unsigned int cpuset_mems_cookie;
 
-        if (in_interrupt() || (gfp & __GFP_THISNODE))
-                pol = &default_policy;
+        if (!in_interrupt() && !(gfp & __GFP_THISNODE))
+                pol = get_task_policy(current);
 
 retry_cpuset:
         cpuset_mems_cookie = read_mems_allowed_begin();