Add cc's.
On 10/22, Peter Zijlstra wrote:
>
> On Wed, Oct 22, 2014 at 06:14:50PM +0200, Oleg Nesterov wrote:
> > Hmm. so perhaps I misunderstood your concern...
> >
> > Do you mean that on !x86 a plain LOAD can "corrupt" the memory as it seen
> > from another vaddr?
>
> I'm not sure. Stores for sure, loads I'm not sure about.
>
> I suspect loads are OK, the aliasing cacheline will be !modified and
> therefore later eviction should discard (not write back). But like said,
> I'm not at all sure.
>
> I would hesitate to put such assumptions into generic code -- although
> it appears we already have.
So perhaps something like this makes sense?
If some arch has problems with D-cache aliasing (because the freed page
can be already mapped by user-space or vmalloc'ed), it can redefine this
helper.
Do you think we can use it to access rq->curr? (although let me repeat
that I won't really argue with SLAB_DESTROY_BY_RCU).
Oleg.
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index ecd3319..eb8494c 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -84,6 +84,22 @@ static inline unsigned long __copy_from_user_nocache(void
*to,
})
/*
+ * @addr is the valid kernel pointer but this memory can be freed.
+ */
+#ifndef probe_slab_address
+#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
+#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;
}
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