mm/mempolicy: fix a race between offset_il_node and mpol_rebind_task

mainline inclusion
from mainline-v5.15-rc1
commit 276aeee1
category: bugfix
bugzilla: 181417 https://gitee.com/openeuler/kernel/issues/I53CSV
backport: openEuler-22.03-LTS

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=276aeee1c5fc00df700f0782060beae126600472

-------------------------------

Servers happened below panic:

  Kernel version:5.4.56
  BUG: unable to handle page fault for address: 0000000000002c48
  RIP: 0010:__next_zones_zonelist+0x1d/0x40
  Call Trace:
    __alloc_pages_nodemask+0x277/0x310
    alloc_page_interleave+0x13/0x70
    handle_mm_fault+0xf99/0x1390
    __do_page_fault+0x288/0x500
    do_page_fault+0x30/0x110
    page_fault+0x3e/0x50

The reason for the panic is that MAX_NUMNODES is passed in the third
parameter in __alloc_pages_nodemask(preferred_nid).  So access to
zonelist->zoneref->zone_idx in __next_zones_zonelist will cause a panic.

In offset_il_node(), first_node() returns nid from pol->v.nodes, after
this other threads may chang pol->v.nodes before next_node().  This race
condition will let next_node return MAX_NUMNODES.  So put pol->nodes in
a local variable.

The race condition is between offset_il_node and cpuset_change_task_nodemask:

  CPU0:                                     CPU1:
  alloc_pages_vma()
    interleave_nid(pol,)
      offset_il_node(pol,)
        first_node(pol->v.nodes)            cpuset_change_task_nodemask
                        //nodes==0xc          mpol_rebind_task
                                                mpol_rebind_policy
                                                  mpol_rebind_nodemask(pol,nodes)
                        //nodes==0x3
        next_node(nid, pol->v.nodes)//return MAX_NUMNODES

Link: https://lkml.kernel.org/r/20210906034658.48721-1-yanghui.def@bytedance.comSigned-off-by: Nyanghui <yanghui.def@bytedance.com>
Reviewed-by: NMuchun Song <songmuchun@bytedance.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 276aeee1)
conflicts:
	mm/mempolicy.c
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

mm/mempolicy.c

@@ -2014,17 +2014,26 @@ unsigned int mempolicy_slab_node(void)
  */
 static unsigned offset_il_node(struct mempolicy *pol, unsigned long n)
 {
-	unsigned nnodes = nodes_weight(pol->v.nodes);
-	unsigned target;
+	nodemask_t nodemask = pol->v.nodes;
+	unsigned int target, nnodes;
 	int i;
 	int nid;
+	/*
+	 * The barrier will stabilize the nodemask in a register or on
+	 * the stack so that it will stop changing under the code.
+	 *
+	 * Between first_node() and next_node(), pol->nodes could be changed
+	 * by other threads. So we put pol->nodes in a local stack.
+	 */
+	barrier();
 
+	nnodes = nodes_weight(nodemask);
 	if (!nnodes)
 		return numa_node_id();
 	target = (unsigned int)n % nnodes;
-	nid = first_node(pol->v.nodes);
+	nid = first_node(nodemask);
 	for (i = 0; i < target; i++)
-		nid = next_node(nid, pol->v.nodes);
+		nid = next_node(nid, nodemask);
 	return nid;
 }