From d4d84fef6d0366b585b7de13527a0faeca84d9ce Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Thu, 2 Jun 2011 10:19:41 -0400 Subject: [PATCH] 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 Acked-by: Christoph Lameter Signed-off-by: Chris Metcalf Signed-off-by: Pekka Enberg --- include/linux/percpu.h | 3 +++ mm/slub.c | 12 ++++-------- 2 files changed, 7 insertions(+), 8 deletions(-) diff --git a/include/linux/percpu.h b/include/linux/percpu.h index 8b97308e65df..9ca008f0c542 100644 --- a/include/linux/percpu.h +++ b/include/linux/percpu.h @@ -259,6 +259,9 @@ extern void __bad_size_call_parameter(void); * Special handling for cmpxchg_double. cmpxchg_double is passed two * percpu variables. The first has to be aligned to a double word * boundary and the second has to follow directly thereafter. + * We enforce this on all architectures even if they don't support + * a double cmpxchg instruction, since it's a cheap requirement, and it + * avoids breaking the requirement for architectures with the instruction. */ #define __pcpu_double_call_return_bool(stem, pcp1, pcp2, ...) \ ({ \ 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; -- 2.39.2