[PATCH v4] slab/mempolicy: always use local policy from interrupt context

[PATCH v4] slab/mempolicy: always use local policy from interrupt context

[David Mackey]

From: Andi Kleen <ak@linux.intel.com>

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 patch logic and avoid dereference of current 
task if in interrupt context.]
Signed-off-by: David Mackey <tdmackey@twitter.com>
---
 include/linux/mempolicy.h |    2 +-
 mm/mempolicy.c            |    4 +++-
 mm/slab.c                 |    4 ++--
 mm/slub.c                 |    2 +-
 4 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 4aa4273..95b738c 100644
--- a/include/linux/mempolicy.h
+++ b/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;
 
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index f15c1b2..65801a0 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1602,8 +1602,10 @@ 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 = in_interrupt() ? NULL : current->mempolicy;
+	
 	if (!policy || policy->flags & MPOL_F_LOCAL)
 		return numa_node_id();
 
diff --git a/mm/slab.c b/mm/slab.c
index e901a36..af3b405 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3336,7 +3336,7 @@ 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;
@@ -3368,7 +3368,7 @@ 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:
 	/*
diff --git a/mm/slub.c b/mm/slub.c
index 80848cd..b4f23ad 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1614,7 +1614,7 @@ static struct page *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;
 
-- 
1.7.7.6

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Re: [PATCH v4] slab/mempolicy: always use local policy from interrupt context

[Andi Kleen]

> [tdmackey@twitter.com: Rework patch logic and avoid dereference of current 
> task if in interrupt context.]

avoiding this reference doesn't make sense, it's totally valid.
This is based on a older version. I sent the fixed one some time ago.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only

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Re: [PATCH v4] slab/mempolicy: always use local policy from interrupt context

[KOSAKI Motohiro]

On Thu, May 31, 2012 at 12:22 AM, Andi Kleen <ak@linux.intel.com> wrote:
>> [tdmackey@twitter.com: Rework patch logic and avoid dereference of current
>> task if in interrupt context.]
>
> avoiding this reference doesn't make sense, it's totally valid.
> This is based on a older version. I sent the fixed one some time ago.

Where? I think David's version is most cleaner one.

 Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

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Re: [PATCH v4] slab/mempolicy: always use local policy from interrupt context

[Pekka Enberg]

On Thu, May 31, 2012 at 12:22 AM, Andi Kleen <ak@linux.intel.com> wrote:
>>> [tdmackey@twitter.com: Rework patch logic and avoid dereference of current
>>> task if in interrupt context.]
>>
>> avoiding this reference doesn't make sense, it's totally valid.
>> This is based on a older version. I sent the fixed one some time ago.

On Thu, May 31, 2012 at 7:59 AM, KOSAKI Motohiro
<kosaki.motohiro@gmail.com> wrote:
> Where? I think David's version is most cleaner one.
>
>  Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

Monsieur Lameter, Monsieur Rientjes, ACK/NAK?

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Re: [PATCH v4] slab/mempolicy: always use local policy from interrupt context

[David Rientjes]

On Wed, 30 May 2012, David Mackey wrote:

> From: Andi Kleen <ak@linux.intel.com>
> 
> 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 patch logic and avoid dereference of current 
> task if in interrupt context.]
> Signed-off-by: David Mackey <tdmackey@twitter.com>

Acked-by: David Rientjes <rientjes@google.com>

Thanks for following up on this.

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