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slub: tid must be retrieved from the percpu area of the current processor

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As Steven Rostedt has pointer out: rescheduling could occur on a
different processor after the determination of the per cpu pointer and
before the tid is retrieved. This could result in allocation from the
wrong node in slab_alloc().

The effect is much more severe in slab_free() where we could free to the
freelist of the wrong page.

The window for something like that occurring is pretty small but it is
possible.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
This commit is contained in:
Christoph Lameter 2013-01-23 21:45:48 +00:00 committed by Pekka Enberg
parent 4d7868e647
commit 7cccd80b43
1 changed files with 9 additions and 3 deletions
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12
mm/slub.c
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@ -2332,13 +2332,18 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
s = memcg_kmem_get_cache(s, gfpflags);
redo:
/*
* Must read kmem_cache cpu data via this cpu ptr. Preemption is
* enabled. We may switch back and forth between cpus while
* reading from one cpu area. That does not matter as long
* as we end up on the original cpu again when doing the cmpxchg.
*
* Preemption is disabled for the retrieval of the tid because that
* must occur from the current processor. We cannot allow rescheduling
* on a different processor between the determination of the pointer
* and the retrieval of the tid.
*/
preempt_disable();
c = __this_cpu_ptr(s->cpu_slab);
/*
@ -2348,7 +2353,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
* linked list in between.
*/
tid = c->tid;
barrier();
preempt_enable();
object = c->freelist;
page = c->page;
@ -2595,10 +2600,11 @@ static __always_inline void slab_free(struct kmem_cache *s,
* data is retrieved via this pointer. If we are on the same cpu
* during the cmpxchg then the free will succedd.
*/
preempt_disable();
c = __this_cpu_ptr(s->cpu_slab);
tid = c->tid;
barrier();
preempt_enable();
if (likely(page == c->page)) {
set_freepointer(s, object, c->freelist);