slab: fix generic PAGE_POISONING conflict with SLAB_RED_ZONE
A generic page poisoning mechanism was added with commit:
6a11f75b6a17b5d9ac5025f8d048382fd1f47377
which destructively poisons full pages with a bitpattern.
On arches where PAGE_POISONING is used, this conflicts with the slab
redzone checking enabled by DEBUG_SLAB, scribbling bits all over its
magic words and making it complain about that quite emphatically.
On x86 (and I presume at present all the other arches which set
ARCH_SUPPORTS_DEBUG_PAGEALLOC too), the kernel_map_pages() operation
is non destructive so it can coexist with the other DEBUG_SLAB
mechanisms just fine.
This patch favours the expensive full page destruction test for
cases where there is a collision and it is explicitly selected.
Signed-off-by: Ron Lee <ron@debian.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
diff --git a/mm/slab.c b/mm/slab.c
index 9a90b00..1a6040d 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2353,6 +2353,15 @@
/* really off slab. No need for manual alignment */
slab_size =
cachep->num * sizeof(kmem_bufctl_t) + sizeof(struct slab);
+
+#ifdef CONFIG_PAGE_POISONING
+ /* If we're going to use the generic kernel_map_pages()
+ * poisoning, then it's going to smash the contents of
+ * the redzone and userword anyhow, so switch them off.
+ */
+ if (size % PAGE_SIZE == 0 && flags & SLAB_POISON)
+ flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
+#endif
}
cachep->colour_off = cache_line_size();