From 149daaf3a02c020ddae64668c3a1bd0c4f314d6a Mon Sep 17 00:00:00 2001 From: Laura Abbott Date: Tue, 15 Mar 2016 14:55:09 -0700 Subject: [PATCH] slub: relax CMPXCHG consistency restrictions When debug options are enabled, cmpxchg on the page is disabled. This is because the page must be locked to ensure there are no false positives when performing consistency checks. Some debug options such as poisoning and red zoning only act on the object itself. There is no need to protect other CPUs from modification on only the object. Allow cmpxchg to happen with poisoning and red zoning are set on a slab. Credit to Mathias Krause for the original work which inspired this series Signed-off-by: Laura Abbott Acked-by: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Kees Cook Cc: Mathias Krause Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 9cde663bbb10..c2a227d8a4ee 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -163,6 +163,14 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s) #define DEBUG_DEFAULT_FLAGS (SLAB_CONSISTENCY_CHECKS | SLAB_RED_ZONE | \ SLAB_POISON | SLAB_STORE_USER) +/* + * These debug flags cannot use CMPXCHG because there might be consistency + * issues when checking or reading debug information + */ +#define SLAB_NO_CMPXCHG (SLAB_CONSISTENCY_CHECKS | SLAB_STORE_USER | \ + SLAB_TRACE) + + /* * Debugging flags that require metadata to be stored in the slab. These get * disabled when slub_debug=O is used and a cache's min order increases with @@ -3338,7 +3346,7 @@ static int kmem_cache_open(struct kmem_cache *s, unsigned long flags) #if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \ defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) - if (system_has_cmpxchg_double() && (s->flags & SLAB_DEBUG_FLAGS) == 0) + if (system_has_cmpxchg_double() && (s->flags & SLAB_NO_CMPXCHG) == 0) /* Enable fast mode */ s->flags |= __CMPXCHG_DOUBLE; #endif @@ -4846,7 +4854,6 @@ static ssize_t red_zone_store(struct kmem_cache *s, s->flags &= ~SLAB_RED_ZONE; if (buf[0] == '1') { - s->flags &= ~__CMPXCHG_DOUBLE; s->flags |= SLAB_RED_ZONE; } calculate_sizes(s, -1); @@ -4867,7 +4874,6 @@ static ssize_t poison_store(struct kmem_cache *s, s->flags &= ~SLAB_POISON; if (buf[0] == '1') { - s->flags &= ~__CMPXCHG_DOUBLE; s->flags |= SLAB_POISON; } calculate_sizes(s, -1); -- 2.20.1