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Subject[PATCH 2/3] introduce probe_slab_address()
Extract the ifdef(CONFIG_DEBUG_PAGEALLOC) code from get_freepointer_safe()
into the new generic helper, probe_slab_address(). The next patch will add
another user.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
include/linux/uaccess.h | 15 +++++++++++++++
mm/slub.c | 6 +-----
2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index effb637..3367396 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -71,6 +71,21 @@ static inline unsigned long __copy_from_user_nocache(void *to,
__probe_kernel_read(&(retval), (__force void *)(addr), sizeof(retval))

/*
+ * Same as probe_kernel_address(), but @addr must be the valid pointer
+ * to a slab object, potentially freed/reused/unmapped.
+ */
+#ifdef CONFIG_DEBUG_PAGEALLOC
+#define probe_slab_address(addr, retval) \
+ probe_kernel_address(addr, retval)
+#else
+#define probe_slab_address(addr, retval) \
+ ({ \
+ (retval) = *(typeof(retval) *)(addr); \
+ 0; \
+ })
+#endif
+
+/*
* probe_kernel_read(): safely attempt to read from a location
* @dst: pointer to the buffer that shall take the data
* @src: address to read from
diff --git a/mm/slub.c b/mm/slub.c
index 3e8afcc..0467d22 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -265,11 +265,7 @@ 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
+ probe_slab_address(object + s->offset, p);
return p;
}

--
1.5.5.1



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