Commit 5f0d5a3a authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU



A group of Linux kernel hackers reported chasing a bug that resulted
from their assumption that SLAB_DESTROY_BY_RCU provided an existence
guarantee, that is, that no block from such a slab would be reallocated
during an RCU read-side critical section.  Of course, that is not the
case.  Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire
slab of blocks.

However, there is a phrase for this, namely "type safety".  This commit
therefore renames SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU in order
to avoid future instances of this sort of confusion.
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
[ paulmck: Add comments mentioning the old name, as requested by Eric
  Dumazet, in order to help people familiar with the old name find
  the new one. ]
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
parent 4495c08e
......@@ -17,7 +17,7 @@ rcu_dereference.txt
rcubarrier.txt
- RCU and Unloadable Modules
rculist_nulls.txt
- RCU list primitives for use with SLAB_DESTROY_BY_RCU
- RCU list primitives for use with SLAB_TYPESAFE_BY_RCU
rcuref.txt
- Reference-count design for elements of lists/arrays protected by RCU
rcu.txt
......
Using hlist_nulls to protect read-mostly linked lists and
objects using SLAB_DESTROY_BY_RCU allocations.
objects using SLAB_TYPESAFE_BY_RCU allocations.
Please read the basics in Documentation/RCU/listRCU.txt
......@@ -7,7 +7,7 @@ Using special makers (called 'nulls') is a convenient way
to solve following problem :
A typical RCU linked list managing objects which are
allocated with SLAB_DESTROY_BY_RCU kmem_cache can
allocated with SLAB_TYPESAFE_BY_RCU kmem_cache can
use following algos :
1) Lookup algo
......@@ -96,7 +96,7 @@ unlock_chain(); // typically a spin_unlock()
3) Remove algo
--------------
Nothing special here, we can use a standard RCU hlist deletion.
But thanks to SLAB_DESTROY_BY_RCU, beware a deleted object can be reused
But thanks to SLAB_TYPESAFE_BY_RCU, beware a deleted object can be reused
very very fast (before the end of RCU grace period)
if (put_last_reference_on(obj) {
......
......@@ -925,7 +925,8 @@ d. Do you need RCU grace periods to complete even in the face
e. Is your workload too update-intensive for normal use of
RCU, but inappropriate for other synchronization mechanisms?
If so, consider SLAB_DESTROY_BY_RCU. But please be careful!
If so, consider SLAB_TYPESAFE_BY_RCU (which was originally
named SLAB_DESTROY_BY_RCU). But please be careful!
f. Do you need read-side critical sections that are respected
even though they are in the middle of the idle loop, during
......
......@@ -4552,7 +4552,7 @@ i915_gem_load_init(struct drm_i915_private *dev_priv)
dev_priv->requests = KMEM_CACHE(drm_i915_gem_request,
SLAB_HWCACHE_ALIGN |
SLAB_RECLAIM_ACCOUNT |
SLAB_DESTROY_BY_RCU);
SLAB_TYPESAFE_BY_RCU);
if (!dev_priv->requests)
goto err_vmas;
......
......@@ -493,7 +493,7 @@ static inline struct drm_i915_gem_request *
__i915_gem_active_get_rcu(const struct i915_gem_active *active)
{
/* Performing a lockless retrieval of the active request is super
* tricky. SLAB_DESTROY_BY_RCU merely guarantees that the backing
* tricky. SLAB_TYPESAFE_BY_RCU merely guarantees that the backing
* slab of request objects will not be freed whilst we hold the
* RCU read lock. It does not guarantee that the request itself
* will not be freed and then *reused*. Viz,
......
......@@ -1071,7 +1071,7 @@ int ldlm_init(void)
ldlm_lock_slab = kmem_cache_create("ldlm_locks",
sizeof(struct ldlm_lock), 0,
SLAB_HWCACHE_ALIGN |
SLAB_DESTROY_BY_RCU, NULL);
SLAB_TYPESAFE_BY_RCU, NULL);
if (!ldlm_lock_slab) {
kmem_cache_destroy(ldlm_resource_slab);
return -ENOMEM;
......
......@@ -2340,7 +2340,7 @@ static int jbd2_journal_init_journal_head_cache(void)
jbd2_journal_head_cache = kmem_cache_create("jbd2_journal_head",
sizeof(struct journal_head),
0, /* offset */
SLAB_TEMPORARY | SLAB_DESTROY_BY_RCU,
SLAB_TEMPORARY | SLAB_TYPESAFE_BY_RCU,
NULL); /* ctor */
retval = 0;
if (!jbd2_journal_head_cache) {
......
......@@ -38,7 +38,7 @@ void signalfd_cleanup(struct sighand_struct *sighand)
/*
* The lockless check can race with remove_wait_queue() in progress,
* but in this case its caller should run under rcu_read_lock() and
* sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return.
* sighand_cachep is SLAB_TYPESAFE_BY_RCU, we can safely return.
*/
if (likely(!waitqueue_active(wqh)))
return;
......
......@@ -229,7 +229,7 @@ static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence)
*
* Function returns NULL if no refcount could be obtained, or the fence.
* This function handles acquiring a reference to a fence that may be
* reallocated within the RCU grace period (such as with SLAB_DESTROY_BY_RCU),
* reallocated within the RCU grace period (such as with SLAB_TYPESAFE_BY_RCU),
* so long as the caller is using RCU on the pointer to the fence.
*
* An alternative mechanism is to employ a seqlock to protect a bunch of
......@@ -257,7 +257,7 @@ dma_fence_get_rcu_safe(struct dma_fence * __rcu *fencep)
* have successfully acquire a reference to it. If it no
* longer matches, we are holding a reference to some other
* reallocated pointer. This is possible if the allocator
* is using a freelist like SLAB_DESTROY_BY_RCU where the
* is using a freelist like SLAB_TYPESAFE_BY_RCU where the
* fence remains valid for the RCU grace period, but it
* may be reallocated. When using such allocators, we are
* responsible for ensuring the reference we get is to
......
......@@ -28,7 +28,7 @@
#define SLAB_STORE_USER 0x00010000UL /* DEBUG: Store the last owner for bug hunting */
#define SLAB_PANIC 0x00040000UL /* Panic if kmem_cache_create() fails */
/*
* SLAB_DESTROY_BY_RCU - **WARNING** READ THIS!
* SLAB_TYPESAFE_BY_RCU - **WARNING** READ THIS!
*
* This delays freeing the SLAB page by a grace period, it does _NOT_
* delay object freeing. This means that if you do kmem_cache_free()
......@@ -61,8 +61,10 @@
*
* rcu_read_lock before reading the address, then rcu_read_unlock after
* taking the spinlock within the structure expected at that address.
*
* Note that SLAB_TYPESAFE_BY_RCU was originally named SLAB_DESTROY_BY_RCU.
*/
#define SLAB_DESTROY_BY_RCU 0x00080000UL /* Defer freeing slabs to RCU */
#define SLAB_TYPESAFE_BY_RCU 0x00080000UL /* Defer freeing slabs to RCU */
#define SLAB_MEM_SPREAD 0x00100000UL /* Spread some memory over cpuset */
#define SLAB_TRACE 0x00200000UL /* Trace allocations and frees */
......
......@@ -993,7 +993,7 @@ struct smc_hashinfo;
struct module;
/*
* caches using SLAB_DESTROY_BY_RCU should let .next pointer from nulls nodes
* caches using SLAB_TYPESAFE_BY_RCU should let .next pointer from nulls nodes
* un-modified. Special care is taken when initializing object to zero.
*/
static inline void sk_prot_clear_nulls(struct sock *sk, int size)
......
......@@ -1313,7 +1313,7 @@ void __cleanup_sighand(struct sighand_struct *sighand)
if (atomic_dec_and_test(&sighand->count)) {
signalfd_cleanup(sighand);
/*
* sighand_cachep is SLAB_DESTROY_BY_RCU so we can free it
* sighand_cachep is SLAB_TYPESAFE_BY_RCU so we can free it
* without an RCU grace period, see __lock_task_sighand().
*/
kmem_cache_free(sighand_cachep, sighand);
......@@ -2144,7 +2144,7 @@ void __init proc_caches_init(void)
{
sighand_cachep = kmem_cache_create("sighand_cache",
sizeof(struct sighand_struct), 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
SLAB_NOTRACK|SLAB_ACCOUNT, sighand_ctor);
signal_cachep = kmem_cache_create("signal_cache",
sizeof(struct signal_struct), 0,
......
......@@ -1237,7 +1237,7 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
}
/*
* This sighand can be already freed and even reused, but
* we rely on SLAB_DESTROY_BY_RCU and sighand_ctor() which
* we rely on SLAB_TYPESAFE_BY_RCU and sighand_ctor() which
* initializes ->siglock: this slab can't go away, it has
* the same object type, ->siglock can't be reinitialized.
*
......
......@@ -413,7 +413,7 @@ void kasan_cache_create(struct kmem_cache *cache, size_t *size,
*size += sizeof(struct kasan_alloc_meta);
/* Add free meta. */
if (cache->flags & SLAB_DESTROY_BY_RCU || cache->ctor ||
if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
cache->object_size < sizeof(struct kasan_free_meta)) {
cache->kasan_info.free_meta_offset = *size;
*size += sizeof(struct kasan_free_meta);
......@@ -561,7 +561,7 @@ static void kasan_poison_slab_free(struct kmem_cache *cache, void *object)
unsigned long rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
/* RCU slabs could be legally used after free within the RCU period */
if (unlikely(cache->flags & SLAB_DESTROY_BY_RCU))
if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
return;
kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
......@@ -572,7 +572,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)
s8 shadow_byte;
/* RCU slabs could be legally used after free within the RCU period */
if (unlikely(cache->flags & SLAB_DESTROY_BY_RCU))
if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
return false;
shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
......
......@@ -95,7 +95,7 @@ void kmemcheck_slab_alloc(struct kmem_cache *s, gfp_t gfpflags, void *object,
void kmemcheck_slab_free(struct kmem_cache *s, void *object, size_t size)
{
/* TODO: RCU freeing is unsupported for now; hide false positives. */
if (!s->ctor && !(s->flags & SLAB_DESTROY_BY_RCU))
if (!s->ctor && !(s->flags & SLAB_TYPESAFE_BY_RCU))
kmemcheck_mark_freed(object, size);
}
......
......@@ -430,7 +430,7 @@ static void anon_vma_ctor(void *data)
void __init anon_vma_init(void)
{
anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
0, SLAB_DESTROY_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT,
0, SLAB_TYPESAFE_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT,
anon_vma_ctor);
anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain,
SLAB_PANIC|SLAB_ACCOUNT);
......@@ -481,7 +481,7 @@ struct anon_vma *page_get_anon_vma(struct page *page)
* If this page is still mapped, then its anon_vma cannot have been
* freed. But if it has been unmapped, we have no security against the
* anon_vma structure being freed and reused (for another anon_vma:
* SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()
* SLAB_TYPESAFE_BY_RCU guarantees that - so the atomic_inc_not_zero()
* above cannot corrupt).
*/
if (!page_mapped(page)) {
......
......@@ -1728,7 +1728,7 @@ static void slab_destroy(struct kmem_cache *cachep, struct page *page)
freelist = page->freelist;
slab_destroy_debugcheck(cachep, page);
if (unlikely(cachep->flags & SLAB_DESTROY_BY_RCU))
if (unlikely(cachep->flags & SLAB_TYPESAFE_BY_RCU))
call_rcu(&page->rcu_head, kmem_rcu_free);
else
kmem_freepages(cachep, page);
......@@ -1924,7 +1924,7 @@ static bool set_objfreelist_slab_cache(struct kmem_cache *cachep,
cachep->num = 0;
if (cachep->ctor || flags & SLAB_DESTROY_BY_RCU)
if (cachep->ctor || flags & SLAB_TYPESAFE_BY_RCU)
return false;
left = calculate_slab_order(cachep, size,
......@@ -2030,7 +2030,7 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
if (size < 4096 || fls(size - 1) == fls(size-1 + REDZONE_ALIGN +
2 * sizeof(unsigned long long)))
flags |= SLAB_RED_ZONE | SLAB_STORE_USER;
if (!(flags & SLAB_DESTROY_BY_RCU))
if (!(flags & SLAB_TYPESAFE_BY_RCU))
flags |= SLAB_POISON;
#endif
#endif
......
......@@ -126,7 +126,7 @@ static inline unsigned long kmem_cache_flags(unsigned long object_size,
/* Legal flag mask for kmem_cache_create(), for various configurations */
#define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | SLAB_PANIC | \
SLAB_DESTROY_BY_RCU | SLAB_DEBUG_OBJECTS )
SLAB_TYPESAFE_BY_RCU | SLAB_DEBUG_OBJECTS )
#if defined(CONFIG_DEBUG_SLAB)
#define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)
......@@ -415,7 +415,7 @@ static inline size_t slab_ksize(const struct kmem_cache *s)
* back there or track user information then we can
* only use the space before that information.
*/
if (s->flags & (SLAB_DESTROY_BY_RCU | SLAB_STORE_USER))
if (s->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_STORE_USER))
return s->inuse;
/*
* Else we can use all the padding etc for the allocation
......
......@@ -39,7 +39,7 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
* Set of flags that will prevent slab merging
*/
#define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
SLAB_TRACE | SLAB_DESTROY_BY_RCU | SLAB_NOLEAKTRACE | \
SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \
SLAB_FAILSLAB | SLAB_KASAN)
#define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
......@@ -500,7 +500,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
struct kmem_cache *s, *s2;
/*
* On destruction, SLAB_DESTROY_BY_RCU kmem_caches are put on the
* On destruction, SLAB_TYPESAFE_BY_RCU kmem_caches are put on the
* @slab_caches_to_rcu_destroy list. The slab pages are freed
* through RCU and and the associated kmem_cache are dereferenced
* while freeing the pages, so the kmem_caches should be freed only
......@@ -537,7 +537,7 @@ static int shutdown_cache(struct kmem_cache *s)
memcg_unlink_cache(s);
list_del(&s->list);
if (s->flags & SLAB_DESTROY_BY_RCU) {
if (s->flags & SLAB_TYPESAFE_BY_RCU) {
list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
schedule_work(&slab_caches_to_rcu_destroy_work);
} else {
......
......@@ -126,7 +126,7 @@ static inline void clear_slob_page_free(struct page *sp)
/*
* struct slob_rcu is inserted at the tail of allocated slob blocks, which
* were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
* were created with a SLAB_TYPESAFE_BY_RCU slab. slob_rcu is used to free
* the block using call_rcu.
*/
struct slob_rcu {
......@@ -524,7 +524,7 @@ EXPORT_SYMBOL(ksize);
int __kmem_cache_create(struct kmem_cache *c, unsigned long flags)
{
if (flags & SLAB_DESTROY_BY_RCU) {
if (flags & SLAB_TYPESAFE_BY_RCU) {
/* leave room for rcu footer at the end of object */
c->size += sizeof(struct slob_rcu);
}
......@@ -598,7 +598,7 @@ static void kmem_rcu_free(struct rcu_head *head)
void kmem_cache_free(struct kmem_cache *c, void *b)
{
kmemleak_free_recursive(b, c->flags);
if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
if (unlikely(c->flags & SLAB_TYPESAFE_BY_RCU)) {
struct slob_rcu *slob_rcu;
slob_rcu = b + (c->size - sizeof(struct slob_rcu));
slob_rcu->size = c->size;
......
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