slab/mempolicy: always use local policy from interrupt context

slab_node() could access current->mempolicy from interrupt context.
However there's a race condition during exit where the mempolicy
is first freed and then the pointer zeroed.

Using this from interrupts seems bogus anyways. The interrupt
will interrupt a random process and therefore get a random
mempolicy. Many times, this will be idle's, which noone can change.

Just disable this here and always use local for slab
from interrupts. I also cleaned up the callers of slab_node a bit
which always passed the same argument.

I believe the original mempolicy code did that in fact,
so it's likely a regression.

v2: send version with correct logic
v3: simplify. fix typo.
Reported-by: Arun Sharma <asharma@fb.com>
Cc: penberg@kernel.org
Cc: cl@linux.com
Signed-off-by: Andi Kleen <ak@linux.intel.com>
[tdmackey@twitter.com: Rework control flow based on feedback from
cl@linux.com, fix logic, and cleanup current task_struct reference]
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: David Mackey <tdmackey@twitter.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

include/linux/mempolicy.h

@@ -215,7 +215,7 @@ extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
 extern bool init_nodemask_of_mempolicy(nodemask_t *mask);
 extern bool mempolicy_nodemask_intersects(struct task_struct *tsk,
 				const nodemask_t *mask);
-extern unsigned slab_node(struct mempolicy *policy);
+extern unsigned slab_node(void);
 
 extern enum zone_type policy_zone;
 

mm/mempolicy.c

@@ -1602,8 +1602,14 @@ static unsigned interleave_nodes(struct mempolicy *policy)
  * task can change it's policy.  The system default policy requires no
  * such protection.
  */
-unsigned slab_node(struct mempolicy *policy)
+unsigned slab_node(void)
 {
+	struct mempolicy *policy;
+
+	if (in_interrupt())
+		return numa_node_id();
+
+	policy = current->mempolicy;
 	if (!policy || policy->flags & MPOL_F_LOCAL)
 		return numa_node_id();
 

mm/slab.c

@@ -3310,7 +3310,7 @@ static void *alternate_node_alloc(struct kmem_cache *cachep, gfp_t flags)
 	if (cpuset_do_slab_mem_spread() && (cachep->flags & SLAB_MEM_SPREAD))
 		nid_alloc = cpuset_slab_spread_node();
 	else if (current->mempolicy)
-		nid_alloc = slab_node(current->mempolicy);
+		nid_alloc = slab_node();
 	if (nid_alloc != nid_here)
 		return ____cache_alloc_node(cachep, flags, nid_alloc);
 	return NULL;
@@ -3342,7 +3342,7 @@ static void *fallback_alloc(struct kmem_cache *cache, gfp_t flags)
 
 retry_cpuset:
 	cpuset_mems_cookie = get_mems_allowed();
-	zonelist = node_zonelist(slab_node(current->mempolicy), flags);
+	zonelist = node_zonelist(slab_node(), flags);
 
 retry:
 	/*

mm/slub.c

@@ -1617,7 +1617,7 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
 
 	do {
 		cpuset_mems_cookie = get_mems_allowed();
-		zonelist = node_zonelist(slab_node(current->mempolicy), flags);
+		zonelist = node_zonelist(slab_node(), flags);
 		for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
 			struct kmem_cache_node *n;