From: Christoph Lameter <cl@linux.com>
Date: Mon, 16 May 2011 20:26:08 +0000 (-0500)
Subject: slub: Make CONFIG_DEBUG_PAGE_ALLOC work with new fastpath
X-Git-Tag: v2.6.39.1~73
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=440316e6310c2ce372e32d12c83ccc8ddcfb5028;p=karo-tx-linux.git

slub: Make CONFIG_DEBUG_PAGE_ALLOC work with new fastpath

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>
---

diff --git a/mm/slub.c b/mm/slub.c
index 9d2e5e46bf09..f6cb6cd69fcc 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -261,6 +261,18 @@ static inline void *get_freepointer(struct kmem_cache *s, void *object)
 	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;