cpuset,mm: fix no node to alloc memory when changing cpuset's mems

Before applying this patch, cpuset updates task->mems_allowed and
mempolicy by setting all new bits in the nodemask first, and clearing all
old unallowed bits later.  But in the way, the allocator may find that
there is no node to alloc memory.

The reason is that cpuset rebinds the task's mempolicy, it cleans the
nodes which the allocater can alloc pages on, for example:

(mpol: mempolicy)
	task1			task1's mpol	task2
	alloc page		1
	  alloc on node0? NO	1
				1		change mems from 1 to 0
				1		rebind task1's mpol
				0-1		  set new bits
				0	  	  clear disallowed bits
	  alloc on node1? NO	0
	  ...
	can't alloc page
	  goto oom

This patch fixes this problem by expanding the nodes range first(set newly
allowed bits) and shrink it lazily(clear newly disallowed bits).  So we
use a variable to tell the write-side task that read-side task is reading
nodemask, and the write-side task clears newly disallowed nodes after
read-side task ends the current memory allocation.

[akpm@linux-foundation.org: fix spello]
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Paul Menage <menage@google.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Ravikiran Thirumalai <kiran@scalex86.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 4 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 8a993db88029..721b2b338032 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1639,6 +1639,8 @@ static inline unsigned interleave_nid(struct mempolicy *pol,
  * to the struct mempolicy for conditional unref after allocation.
  * If the effective policy is 'BIND, returns a pointer to the mempolicy's
  * @nodemask for filtering the zonelist.
+ *
+ * Must be protected by get_mems_allowed()
  */
 struct zonelist *huge_zonelist(struct vm_area_struct *vma, unsigned long addr,
                                 gfp_t gfp_flags, struct mempolicy **mpol,
@@ -1684,6 +1686,7 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
         if (!(mask && current->mempolicy))
                 return false;
 
+        task_lock(current);
         mempolicy = current->mempolicy;
         switch (mempolicy->mode) {
         case MPOL_PREFERRED:
@@ -1703,6 +1706,7 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
         default:
                 BUG();
         }
+        task_unlock(current);
 
         return true;
 }
@@ -1750,13 +1754,17 @@ alloc_page_vma(gfp_t gfp, struct vm_area_struct *vma, unsigned long addr)
 {
         struct mempolicy *pol = get_vma_policy(current, vma, addr);
         struct zonelist *zl;
+        struct page *page;
 
+        get_mems_allowed();
         if (unlikely(pol->mode == MPOL_INTERLEAVE)) {
                 unsigned nid;
 
                 nid = interleave_nid(pol, vma, addr, PAGE_SHIFT);
                 mpol_cond_put(pol);
-                return alloc_page_interleave(gfp, 0, nid);
+                page = alloc_page_interleave(gfp, 0, nid);
+                put_mems_allowed();
+                return page;
         }
         zl = policy_zonelist(gfp, pol);
         if (unlikely(mpol_needs_cond_ref(pol))) {
@@ -1766,12 +1774,15 @@ alloc_page_vma(gfp_t gfp, struct vm_area_struct *vma, unsigned long addr)
                 struct page *page =  __alloc_pages_nodemask(gfp, 0,
                                                 zl, policy_nodemask(gfp, pol));
                 __mpol_put(pol);
+                put_mems_allowed();
                 return page;
         }
         /*
          * fast path:  default or task policy
          */
-        return __alloc_pages_nodemask(gfp, 0, zl, policy_nodemask(gfp, pol));
+        page = __alloc_pages_nodemask(gfp, 0, zl, policy_nodemask(gfp, pol));
+        put_mems_allowed();
+        return page;
 }
 
 /**
@@ -1796,18 +1807,23 @@ alloc_page_vma(gfp_t gfp, struct vm_area_struct *vma, unsigned long addr)
 struct page *alloc_pages_current(gfp_t gfp, unsigned order)
 {
         struct mempolicy *pol = current->mempolicy;
+        struct page *page;
 
         if (!pol || in_interrupt() || (gfp & __GFP_THISNODE))
                 pol = &default_policy;
 
+        get_mems_allowed();
         /*
          * No reference counting needed for current->mempolicy
          * nor system default_policy
          */
         if (pol->mode == MPOL_INTERLEAVE)
-                return alloc_page_interleave(gfp, order, interleave_nodes(pol));
-        return __alloc_pages_nodemask(gfp, order,
+                page = alloc_page_interleave(gfp, order, interleave_nodes(pol));
+        else
+                page = __alloc_pages_nodemask(gfp, order,
                         policy_zonelist(gfp, pol), policy_nodemask(gfp, pol));
+        put_mems_allowed();
+        return page;
 }
 EXPORT_SYMBOL(alloc_pages_current);