[PATCH] slub: Make CONFIG_PAGE_ALLOC work with new fastpath

Christoph Lameter
2011-05-13T21:15:45Z

I ran this with hackbench under KVM with CONFIG_DEBUG_PAGEALLOC and I saw
no failures.

Subject: slub: Make CONFIG_PAGE_ALLOC work with new fastpath

Fastpath can do a speculative access to a page that CONFIG_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.

Signed-off-by: Christoph Lameter <cl@linux.com>
---
mm/slub.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2011-05-10 14:31:28.000000000 -0500
+++ linux-2.6/mm/slub.c 2011-05-10 14:31:35.000000000 -0500
@@ -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;
@@ -1933,7 +1945,7 @@ 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;