Slab allocators: Drop support for destructors
There is no user of destructors left. There is no reason why we should keep
checking for destructors calls in the slab allocators.
The RFC for this patch was discussed at
http://marc.info/?l=linux-kernel&m=117882364330705&w=2
Destructors were mainly used for list management which required them to take a
spinlock. Taking a spinlock in a destructor is a bit risky since the slab
allocators may run the destructors anytime they decide a slab is no longer
needed.
Patch drops destructor support. Any attempt to use a destructor will BUG().
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index c6c1f4a..5e2e729 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -40,7 +40,6 @@
int objects; /* Number of objects in slab */
int refcount; /* Refcount for slab cache destroy */
void (*ctor)(void *, struct kmem_cache *, unsigned long);
- void (*dtor)(void *, struct kmem_cache *, unsigned long);
int inuse; /* Offset to metadata */
int align; /* Alignment */
const char *name; /* Name (only for display!) */
diff --git a/mm/slab.c b/mm/slab.c
index 944b205..1234443 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -409,9 +409,6 @@
/* constructor func */
void (*ctor) (void *, struct kmem_cache *, unsigned long);
- /* de-constructor func */
- void (*dtor) (void *, struct kmem_cache *, unsigned long);
-
/* 5) cache creation/removal */
const char *name;
struct list_head next;
@@ -1911,20 +1908,11 @@
slab_error(cachep, "end of a freed object "
"was overwritten");
}
- if (cachep->dtor && !(cachep->flags & SLAB_POISON))
- (cachep->dtor) (objp + obj_offset(cachep), cachep, 0);
}
}
#else
static void slab_destroy_objs(struct kmem_cache *cachep, struct slab *slabp)
{
- if (cachep->dtor) {
- int i;
- for (i = 0; i < cachep->num; i++) {
- void *objp = index_to_obj(cachep, slabp, i);
- (cachep->dtor) (objp, cachep, 0);
- }
- }
}
#endif
@@ -2124,7 +2112,7 @@
* @align: The required alignment for the objects.
* @flags: SLAB flags
* @ctor: A constructor for the objects.
- * @dtor: A destructor for the objects.
+ * @dtor: A destructor for the objects (not implemented anymore).
*
* Returns a ptr to the cache on success, NULL on failure.
* Cannot be called within a int, but can be interrupted.
@@ -2159,7 +2147,7 @@
* Sanity checks... these are all serious usage bugs.
*/
if (!name || in_interrupt() || (size < BYTES_PER_WORD) ||
- (size > (1 << MAX_OBJ_ORDER) * PAGE_SIZE) || (dtor && !ctor)) {
+ (size > (1 << MAX_OBJ_ORDER) * PAGE_SIZE) || dtor) {
printk(KERN_ERR "%s: Early error in slab %s\n", __FUNCTION__,
name);
BUG();
@@ -2213,9 +2201,6 @@
if (flags & SLAB_DESTROY_BY_RCU)
BUG_ON(flags & SLAB_POISON);
#endif
- if (flags & SLAB_DESTROY_BY_RCU)
- BUG_ON(dtor);
-
/*
* Always checks flags, a caller might be expecting debug support which
* isn't available.
@@ -2370,7 +2355,6 @@
BUG_ON(!cachep->slabp_cache);
}
cachep->ctor = ctor;
- cachep->dtor = dtor;
cachep->name = name;
if (setup_cpu_cache(cachep)) {
@@ -2835,7 +2819,6 @@
* Perform extra freeing checks:
* - detect bad pointers.
* - POISON/RED_ZONE checking
- * - destructor calls, for caches with POISON+dtor
*/
static void kfree_debugcheck(const void *objp)
{
@@ -2894,12 +2877,6 @@
BUG_ON(objnr >= cachep->num);
BUG_ON(objp != index_to_obj(cachep, slabp, objnr));
- if (cachep->flags & SLAB_POISON && cachep->dtor) {
- /* we want to cache poison the object,
- * call the destruction callback
- */
- cachep->dtor(objp + obj_offset(cachep), cachep, 0);
- }
#ifdef CONFIG_DEBUG_SLAB_LEAK
slab_bufctl(slabp)[objnr] = BUFCTL_FREE;
#endif
diff --git a/mm/slob.c b/mm/slob.c
index 57bb72e..79164a4 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -280,7 +280,6 @@
unsigned long flags;
const char *name;
void (*ctor)(void *, struct kmem_cache *, unsigned long);
- void (*dtor)(void *, struct kmem_cache *, unsigned long);
};
struct kmem_cache *kmem_cache_create(const char *name, size_t size,
@@ -296,13 +295,11 @@
c->name = name;
c->size = size;
if (flags & SLAB_DESTROY_BY_RCU) {
- BUG_ON(dtor);
/* leave room for rcu footer at the end of object */
c->size += sizeof(struct slob_rcu);
}
c->flags = flags;
c->ctor = ctor;
- c->dtor = dtor;
/* ignore alignment unless it's forced */
c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
if (c->align < align)
@@ -371,8 +368,6 @@
slob_rcu->size = c->size;
call_rcu(&slob_rcu->head, kmem_rcu_free);
} else {
- if (c->dtor)
- c->dtor(b, c, 0);
__kmem_cache_free(b, c->size);
}
}
diff --git a/mm/slub.c b/mm/slub.c
index 5e3e8bc..022c1b4 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -891,13 +891,13 @@
* On 32 bit platforms the limit is 256k. On 64bit platforms
* the limit is 512k.
*
- * Debugging or ctor/dtors may create a need to move the free
+ * Debugging or ctor may create a need to move the free
* pointer. Fail if this happens.
*/
if (s->size >= 65535 * sizeof(void *)) {
BUG_ON(s->flags & (SLAB_RED_ZONE | SLAB_POISON |
SLAB_STORE_USER | SLAB_DESTROY_BY_RCU));
- BUG_ON(s->ctor || s->dtor);
+ BUG_ON(s->ctor);
}
else
/*
@@ -1030,15 +1030,12 @@
{
int pages = 1 << s->order;
- if (unlikely(SlabDebug(page) || s->dtor)) {
+ if (unlikely(SlabDebug(page))) {
void *p;
slab_pad_check(s, page);
- for_each_object(p, s, page_address(page)) {
- if (s->dtor)
- s->dtor(p, s, 0);
+ for_each_object(p, s, page_address(page))
check_object(s, page, p, 0);
- }
}
mod_zone_page_state(page_zone(page),
@@ -1871,7 +1868,7 @@
* then we should never poison the object itself.
*/
if ((flags & SLAB_POISON) && !(flags & SLAB_DESTROY_BY_RCU) &&
- !s->ctor && !s->dtor)
+ !s->ctor)
s->flags |= __OBJECT_POISON;
else
s->flags &= ~__OBJECT_POISON;
@@ -1901,7 +1898,7 @@
#ifdef CONFIG_SLUB_DEBUG
if (((flags & (SLAB_DESTROY_BY_RCU | SLAB_POISON)) ||
- s->ctor || s->dtor)) {
+ s->ctor)) {
/*
* Relocate free pointer after the object if it is not
* permitted to overwrite the first word of the object on
@@ -1970,13 +1967,11 @@
static int kmem_cache_open(struct kmem_cache *s, gfp_t gfpflags,
const char *name, size_t size,
size_t align, unsigned long flags,
- void (*ctor)(void *, struct kmem_cache *, unsigned long),
- void (*dtor)(void *, struct kmem_cache *, unsigned long))
+ void (*ctor)(void *, struct kmem_cache *, unsigned long))
{
memset(s, 0, kmem_size);
s->name = name;
s->ctor = ctor;
- s->dtor = dtor;
s->objsize = size;
s->flags = flags;
s->align = align;
@@ -2161,7 +2156,7 @@
down_write(&slub_lock);
if (!kmem_cache_open(s, gfp_flags, name, size, ARCH_KMALLOC_MINALIGN,
- flags, NULL, NULL))
+ flags, NULL))
goto panic;
list_add(&s->list, &slab_caches);
@@ -2463,7 +2458,7 @@
if (slub_nomerge || (s->flags & SLUB_NEVER_MERGE))
return 1;
- if (s->ctor || s->dtor)
+ if (s->ctor)
return 1;
return 0;
@@ -2471,15 +2466,14 @@
static struct kmem_cache *find_mergeable(size_t size,
size_t align, unsigned long flags,
- void (*ctor)(void *, struct kmem_cache *, unsigned long),
- void (*dtor)(void *, struct kmem_cache *, unsigned long))
+ void (*ctor)(void *, struct kmem_cache *, unsigned long))
{
struct list_head *h;
if (slub_nomerge || (flags & SLUB_NEVER_MERGE))
return NULL;
- if (ctor || dtor)
+ if (ctor)
return NULL;
size = ALIGN(size, sizeof(void *));
@@ -2521,8 +2515,9 @@
{
struct kmem_cache *s;
+ BUG_ON(dtor);
down_write(&slub_lock);
- s = find_mergeable(size, align, flags, ctor, dtor);
+ s = find_mergeable(size, align, flags, ctor);
if (s) {
s->refcount++;
/*
@@ -2536,7 +2531,7 @@
} else {
s = kmalloc(kmem_size, GFP_KERNEL);
if (s && kmem_cache_open(s, GFP_KERNEL, name,
- size, align, flags, ctor, dtor)) {
+ size, align, flags, ctor)) {
if (sysfs_slab_add(s)) {
kfree(s);
goto err;
@@ -3177,17 +3172,6 @@
}
SLAB_ATTR_RO(ctor);
-static ssize_t dtor_show(struct kmem_cache *s, char *buf)
-{
- if (s->dtor) {
- int n = sprint_symbol(buf, (unsigned long)s->dtor);
-
- return n + sprintf(buf + n, "\n");
- }
- return 0;
-}
-SLAB_ATTR_RO(dtor);
-
static ssize_t aliases_show(struct kmem_cache *s, char *buf)
{
return sprintf(buf, "%d\n", s->refcount - 1);
@@ -3419,7 +3403,6 @@
&partial_attr.attr,
&cpu_slabs_attr.attr,
&ctor_attr.attr,
- &dtor_attr.attr,
&aliases_attr.attr,
&align_attr.attr,
&sanity_checks_attr.attr,