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Subject[093/165] slub: Make CONFIG_DEBUG_PAGE_ALLOC work with new fastpath
2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------
Content-Length: 1498
Lines: 50

From: Christoph Lameter <cl@linux.com>

commit 1393d9a1857471f816d0be1ccc1d6433a86050f6 upstream.

Fastpath can do a speculative access to a page that CONFIG_DEBUG_PAGE_ALLOC may have
marked as invalid to retrieve the pointer to the next free object.

Use probe_kernel_read in that case in order not to cause a page fault.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
mm/slub.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -261,6 +261,18 @@ static inline void *get_freepointer(stru
return *(void **)(object + s->offset);
}

+static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
+{
+ void *p;
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+ probe_kernel_read(&p, (void **)(object + s->offset), sizeof(p));
+#else
+ p = get_freepointer(s, object);
+#endif
+ return p;
+}
+
static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
{
*(void **)(object + s->offset) = fp;
@@ -1943,7 +1955,7 @@ redo:
if (unlikely(!irqsafe_cpu_cmpxchg_double(
s->cpu_slab->freelist, s->cpu_slab->tid,
object, tid,
- get_freepointer(s, object), next_tid(tid)))) {
+ get_freepointer_safe(s, object), next_tid(tid)))) {

note_cmpxchg_failure("slab_alloc", s, tid);
goto redo;



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