slub: always align cpu_slab to honor cmpxchg_double requirement

On an architecture without CMPXCHG_LOCAL but with DEBUG_VM enabled,
the VM_BUG_ON() in __pcpu_double_call_return_bool() will cause an early
panic during boot unless we always align cpu_slab properly.

In principle we could remove the alignment-testing VM_BUG_ON() for
architectures that don't have CMPXCHG_LOCAL, but leaving it in means
that new code will tend not to break x86 even if it is introduced
on another platform, and it's low cost to require alignment.

Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

1 files changed, 4 insertions, 8 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 7be0223531b0..35f351f26193 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2320,16 +2320,12 @@ static inline int alloc_kmem_cache_cpus(struct kmem_cache *s)
         BUILD_BUG_ON(PERCPU_DYNAMIC_EARLY_SIZE <
                         SLUB_PAGE_SHIFT * sizeof(struct kmem_cache_cpu));
 
-#ifdef CONFIG_CMPXCHG_LOCAL
         /*
-         * Must align to double word boundary for the double cmpxchg instructions
-         * to work.
+         * Must align to double word boundary for the double cmpxchg
+         * instructions to work; see __pcpu_double_call_return_bool().
          */
-        s->cpu_slab = __alloc_percpu(sizeof(struct kmem_cache_cpu), 2 * sizeof(void *));
-#else
-        /* Regular alignment is sufficient */
-        s->cpu_slab = alloc_percpu(struct kmem_cache_cpu);
-#endif
+        s->cpu_slab = __alloc_percpu(sizeof(struct kmem_cache_cpu),
+                                     2 * sizeof(void *));
 
         if (!s->cpu_slab)
                 return 0;