[PATCHv2 3/4] slub: Convert SLAB_DEBUG_FREE to SLAB_CONSISTENCY_CHECKS

From: Laura Abbott
Date: Mon Feb 15 2016 - 13:44:57 EST


SLAB_DEBUG_FREE allows expensive consistency checks at free
to be turned on or off. Expand its use to be able to turn
off all consistency checks. This gives a nice speed up if
you only want features such as poisoning or tracing.

Credit to Mathias Krause for the original work which inspired this series

Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
---
Documentation/vm/slub.txt | 4 +-
include/linux/slab.h | 2 +-
mm/slab.h | 5 ++-
mm/slub.c | 94 +++++++++++++++++++++++++++++------------------
tools/vm/slabinfo.c | 2 +-
5 files changed, 66 insertions(+), 41 deletions(-)

diff --git a/Documentation/vm/slub.txt b/Documentation/vm/slub.txt
index f0d3409..8465241 100644
--- a/Documentation/vm/slub.txt
+++ b/Documentation/vm/slub.txt
@@ -35,8 +35,8 @@ slub_debug=<Debug-Options>,<slab name>
Enable options only for select slabs

Possible debug options are
- F Sanity checks on (enables SLAB_DEBUG_FREE. Sorry
- SLAB legacy issues)
+ F Sanity checks on (enables SLAB_DEBUG_CONSISTENCY_CHECKS
+ Sorry SLAB legacy issues)
Z Red zoning
P Poisoning (object and padding)
U User tracking (free and alloc)
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 3627d5c..1070daa 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -20,7 +20,7 @@
* Flags to pass to kmem_cache_create().
* The ones marked DEBUG are only valid if CONFIG_DEBUG_SLAB is set.
*/
-#define SLAB_DEBUG_FREE 0x00000100UL /* DEBUG: Perform (expensive) checks on free */
+#define SLAB_CONSISTENCY_CHECKS 0x00000100UL /* DEBUG: Perform (expensive) checks on alloc/free */
#define SLAB_RED_ZONE 0x00000400UL /* DEBUG: Red zone objs in a cache */
#define SLAB_POISON 0x00000800UL /* DEBUG: Poison objects */
#define SLAB_HWCACHE_ALIGN 0x00002000UL /* Align objs on cache lines */
diff --git a/mm/slab.h b/mm/slab.h
index 834ad24..fca99be 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -121,7 +121,7 @@ static inline unsigned long kmem_cache_flags(unsigned long object_size,
#define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)
#elif defined(CONFIG_SLUB_DEBUG)
#define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
- SLAB_TRACE | SLAB_DEBUG_FREE)
+ SLAB_TRACE | SLAB_CONSISTENCY_CHECKS)
#else
#define SLAB_DEBUG_FLAGS (0)
#endif
@@ -306,7 +306,8 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
* to not do even the assignment. In that case, slab_equal_or_root
* will also be a constant.
*/
- if (!memcg_kmem_enabled() && !unlikely(s->flags & SLAB_DEBUG_FREE))
+ if (!memcg_kmem_enabled() &&
+ !unlikely(s->flags & SLAB_CONSISTENCY_CHECKS))
return s;

page = virt_to_head_page(x);
diff --git a/mm/slub.c b/mm/slub.c
index 189c330..01606ff 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -160,7 +160,7 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
*/
#define MAX_PARTIAL 10

-#define DEBUG_DEFAULT_FLAGS (SLAB_DEBUG_FREE | SLAB_RED_ZONE | \
+#define DEBUG_DEFAULT_FLAGS (SLAB_CONSISTENCY_CHECKS | SLAB_RED_ZONE | \
SLAB_POISON | SLAB_STORE_USER)

/*
@@ -1031,20 +1031,32 @@ static void setup_object_debug(struct kmem_cache *s, struct page *page,
init_tracking(s, object);
}

-static noinline int alloc_debug_processing(struct kmem_cache *s,
+static inline int alloc_consistency_checks(struct kmem_cache *s,
struct page *page,
void *object, unsigned long addr)
{
if (!check_slab(s, page))
- goto bad;
+ return 0;

if (!check_valid_pointer(s, page, object)) {
object_err(s, page, object, "Freelist Pointer check fails");
- goto bad;
+ return 0;
}

if (!check_object(s, page, object, SLUB_RED_INACTIVE))
- goto bad;
+ return 0;
+
+ return 1;
+}
+
+static noinline int alloc_debug_processing(struct kmem_cache *s,
+ struct page *page,
+ void *object, unsigned long addr)
+{
+ if (s->flags & SLAB_CONSISTENCY_CHECKS) {
+ if (!alloc_consistency_checks(s, page, object, addr))
+ goto bad;
+ }

/* Success perform special debug activities for allocs */
if (s->flags & SLAB_STORE_USER)
@@ -1067,39 +1079,21 @@ bad:
return 0;
}

-/* Supports checking bulk free of a constructed freelist */
-static noinline int free_debug_processing(
- struct kmem_cache *s, struct page *page,
- void *head, void *tail, int bulk_cnt,
- unsigned long addr)
+static inline int free_consistency_checks(struct kmem_cache *s,
+ struct page *page, void *object, unsigned long addr)
{
- struct kmem_cache_node *n = get_node(s, page_to_nid(page));
- void *object = head;
- int cnt = 0;
- unsigned long uninitialized_var(flags);
- int ret = 0;
-
- spin_lock_irqsave(&n->list_lock, flags);
- slab_lock(page);
-
- if (!check_slab(s, page))
- goto out;
-
-next_object:
- cnt++;
-
if (!check_valid_pointer(s, page, object)) {
slab_err(s, page, "Invalid object pointer 0x%p", object);
- goto out;
+ return 0;
}

if (on_freelist(s, page, object)) {
object_err(s, page, object, "Object already free");
- goto out;
+ return 0;
}

if (!check_object(s, page, object, SLUB_RED_ACTIVE))
- goto out;
+ return 0;

if (unlikely(s != page->slab_cache)) {
if (!PageSlab(page)) {
@@ -1112,7 +1106,37 @@ next_object:
} else
object_err(s, page, object,
"page slab pointer corrupt.");
- goto out;
+ return 0;
+ }
+ return 1;
+}
+
+/* Supports checking bulk free of a constructed freelist */
+static noinline int free_debug_processing(
+ struct kmem_cache *s, struct page *page,
+ void *head, void *tail, int bulk_cnt,
+ unsigned long addr)
+{
+ struct kmem_cache_node *n = get_node(s, page_to_nid(page));
+ void *object = head;
+ int cnt = 0;
+ unsigned long uninitialized_var(flags);
+ int ret = 0;
+
+ spin_lock_irqsave(&n->list_lock, flags);
+ slab_lock(page);
+
+ if (s->flags & SLAB_CONSISTENCY_CHECKS) {
+ if (!check_slab(s, page))
+ goto out;
+ }
+
+next_object:
+ cnt++;
+
+ if (s->flags & SLAB_CONSISTENCY_CHECKS) {
+ if (!free_consistency_checks(s, page, object, addr))
+ goto out;
}

if (s->flags & SLAB_STORE_USER)
@@ -1169,7 +1193,7 @@ static int __init setup_slub_debug(char *str)
for (; *str && *str != ','; str++) {
switch (tolower(*str)) {
case 'f':
- slub_debug |= SLAB_DEBUG_FREE;
+ slub_debug |= SLAB_CONSISTENCY_CHECKS;
break;
case 'z':
slub_debug |= SLAB_RED_ZONE;
@@ -1503,7 +1527,7 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
int order = compound_order(page);
int pages = 1 << order;

- if (kmem_cache_debug(s)) {
+ if (s->flags & SLAB_CONSISTENCY_CHECKS) {
void *p;

slab_pad_check(s, page);
@@ -4812,16 +4836,16 @@ SLAB_ATTR_RO(total_objects);

static ssize_t sanity_checks_show(struct kmem_cache *s, char *buf)
{
- return sprintf(buf, "%d\n", !!(s->flags & SLAB_DEBUG_FREE));
+ return sprintf(buf, "%d\n", !!(s->flags & SLAB_CONSISTENCY_CHECKS));
}

static ssize_t sanity_checks_store(struct kmem_cache *s,
const char *buf, size_t length)
{
- s->flags &= ~SLAB_DEBUG_FREE;
+ s->flags &= ~SLAB_CONSISTENCY_CHECKS;
if (buf[0] == '1') {
s->flags &= ~__CMPXCHG_DOUBLE;
- s->flags |= SLAB_DEBUG_FREE;
+ s->flags |= SLAB_CONSISTENCY_CHECKS;
}
return length;
}
@@ -5356,7 +5380,7 @@ static char *create_unique_id(struct kmem_cache *s)
*p++ = 'd';
if (s->flags & SLAB_RECLAIM_ACCOUNT)
*p++ = 'a';
- if (s->flags & SLAB_DEBUG_FREE)
+ if (s->flags & SLAB_CONSISTENCY_CHECKS)
*p++ = 'F';
if (!(s->flags & SLAB_NOTRACK))
*p++ = 't';
diff --git a/tools/vm/slabinfo.c b/tools/vm/slabinfo.c
index 86e698d..1889163 100644
--- a/tools/vm/slabinfo.c
+++ b/tools/vm/slabinfo.c
@@ -135,7 +135,7 @@ static void usage(void)
"\nValid debug options (FZPUT may be combined)\n"
"a / A Switch on all debug options (=FZUP)\n"
"- Switch off all debug options\n"
- "f / F Sanity Checks (SLAB_DEBUG_FREE)\n"
+ "f / F Sanity Checks (SLAB_CONSISTENCY_CHECKS)\n"
"z / Z Redzoning\n"
"p / P Poisoning\n"
"u / U Tracking\n"
--
2.5.0