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-rw-r--r--include/linux/rhashtable.h261
1 files changed, 165 insertions, 96 deletions
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 0c9175aeab8a..ccbbafdf5547 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -24,12 +24,27 @@
#include <linux/list_nulls.h>
#include <linux/workqueue.h>
#include <linux/rculist.h>
+#include <linux/bit_spinlock.h>
#include <linux/rhashtable-types.h>
/*
+ * Objects in an rhashtable have an embedded struct rhash_head
+ * which is linked into as hash chain from the hash table - or one
+ * of two or more hash tables when the rhashtable is being resized.
* The end of the chain is marked with a special nulls marks which has
- * the least significant bit set.
+ * the least significant bit set but otherwise stores the address of
+ * the hash bucket. This allows us to be be sure we've found the end
+ * of the right list.
+ * The value stored in the hash bucket has BIT(2) used as a lock bit.
+ * This bit must be atomically set before any changes are made to
+ * the chain. To avoid dereferencing this pointer without clearing
+ * the bit first, we use an opaque 'struct rhash_lock_head *' for the
+ * pointer stored in the bucket. This struct needs to be defined so
+ * that rcu_derefernce() works on it, but it has no content so a
+ * cast is needed for it to be useful. This ensures it isn't
+ * used by mistake with clearing the lock bit first.
*/
+struct rhash_lock_head {};
/* Maximum chain length before rehash
*
@@ -52,8 +67,6 @@
* @nest: Number of bits of first-level nested table.
* @rehash: Current bucket being rehashed
* @hash_rnd: Random seed to fold into hash
- * @locks_mask: Mask to apply before accessing locks[]
- * @locks: Array of spinlocks protecting individual buckets
* @walkers: List of active walkers
* @rcu: RCU structure for freeing the table
* @future_tbl: Table under construction during rehashing
@@ -64,17 +77,71 @@ struct bucket_table {
unsigned int size;
unsigned int nest;
u32 hash_rnd;
- unsigned int locks_mask;
- spinlock_t *locks;
struct list_head walkers;
struct rcu_head rcu;
struct bucket_table __rcu *future_tbl;
- struct rhash_head __rcu *buckets[] ____cacheline_aligned_in_smp;
+ struct rhash_lock_head __rcu *buckets[] ____cacheline_aligned_in_smp;
};
/*
+ * We lock a bucket by setting BIT(1) in the pointer - this is always
+ * zero in real pointers and in the nulls marker.
+ * bit_spin_locks do not handle contention well, but the whole point
+ * of the hashtable design is to achieve minimum per-bucket contention.
+ * A nested hash table might not have a bucket pointer. In that case
+ * we cannot get a lock. For remove and replace the bucket cannot be
+ * interesting and doesn't need locking.
+ * For insert we allocate the bucket if this is the last bucket_table,
+ * and then take the lock.
+ * Sometimes we unlock a bucket by writing a new pointer there. In that
+ * case we don't need to unlock, but we do need to reset state such as
+ * local_bh. For that we have rht_assign_unlock(). As rcu_assign_pointer()
+ * provides the same release semantics that bit_spin_unlock() provides,
+ * this is safe.
+ */
+
+static inline void rht_lock(struct rhash_lock_head **bkt)
+{
+ local_bh_disable();
+ bit_spin_lock(1, (unsigned long *)bkt);
+}
+
+static inline void rht_unlock(struct rhash_lock_head **bkt)
+{
+ bit_spin_unlock(1, (unsigned long *)bkt);
+ local_bh_enable();
+}
+
+static inline void rht_assign_unlock(struct rhash_lock_head **bkt,
+ struct rhash_head *obj)
+{
+ struct rhash_head **p = (struct rhash_head **)bkt;
+
+ rcu_assign_pointer(*p, obj);
+ preempt_enable();
+ __release(bitlock);
+ local_bh_enable();
+}
+
+/*
+ * If 'p' is a bucket head and might be locked:
+ * rht_ptr() returns the address without the lock bit.
+ * rht_ptr_locked() returns the address WITH the lock bit.
+ */
+static inline struct rhash_head __rcu *rht_ptr(const struct rhash_lock_head *p)
+{
+ return (void *)(((unsigned long)p) & ~BIT(1));
+}
+
+static inline struct rhash_lock_head __rcu *rht_ptr_locked(const
+ struct rhash_head *p)
+{
+ return (void *)(((unsigned long)p) | BIT(1));
+}
+
+/*
* NULLS_MARKER() expects a hash value with the low
* bits mostly likely to be significant, and it discards
* the msb.
@@ -206,25 +273,6 @@ static inline bool rht_grow_above_max(const struct rhashtable *ht,
return atomic_read(&ht->nelems) >= ht->max_elems;
}
-/* The bucket lock is selected based on the hash and protects mutations
- * on a group of hash buckets.
- *
- * A maximum of tbl->size/2 bucket locks is allocated. This ensures that
- * a single lock always covers both buckets which may both contains
- * entries which link to the same bucket of the old table during resizing.
- * This allows to simplify the locking as locking the bucket in both
- * tables during resize always guarantee protection.
- *
- * IMPORTANT: When holding the bucket lock of both the old and new table
- * during expansions and shrinking, the old bucket lock must always be
- * acquired first.
- */
-static inline spinlock_t *rht_bucket_lock(const struct bucket_table *tbl,
- unsigned int hash)
-{
- return &tbl->locks[hash & tbl->locks_mask];
-}
-
#ifdef CONFIG_PROVE_LOCKING
int lockdep_rht_mutex_is_held(struct rhashtable *ht);
int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash);
@@ -263,13 +311,13 @@ void rhashtable_free_and_destroy(struct rhashtable *ht,
void *arg);
void rhashtable_destroy(struct rhashtable *ht);
-struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
- unsigned int hash);
-struct rhash_head __rcu **__rht_bucket_nested(const struct bucket_table *tbl,
- unsigned int hash);
-struct rhash_head __rcu **rht_bucket_nested_insert(struct rhashtable *ht,
- struct bucket_table *tbl,
+struct rhash_lock_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
+ unsigned int hash);
+struct rhash_lock_head __rcu **__rht_bucket_nested(const struct bucket_table *tbl,
unsigned int hash);
+struct rhash_lock_head __rcu **rht_bucket_nested_insert(struct rhashtable *ht,
+ struct bucket_table *tbl,
+ unsigned int hash);
#define rht_dereference(p, ht) \
rcu_dereference_protected(p, lockdep_rht_mutex_is_held(ht))
@@ -286,21 +334,21 @@ struct rhash_head __rcu **rht_bucket_nested_insert(struct rhashtable *ht,
#define rht_entry(tpos, pos, member) \
({ tpos = container_of(pos, typeof(*tpos), member); 1; })
-static inline struct rhash_head __rcu *const *rht_bucket(
+static inline struct rhash_lock_head __rcu *const *rht_bucket(
const struct bucket_table *tbl, unsigned int hash)
{
return unlikely(tbl->nest) ? rht_bucket_nested(tbl, hash) :
&tbl->buckets[hash];
}
-static inline struct rhash_head __rcu **rht_bucket_var(
+static inline struct rhash_lock_head __rcu **rht_bucket_var(
struct bucket_table *tbl, unsigned int hash)
{
return unlikely(tbl->nest) ? __rht_bucket_nested(tbl, hash) :
&tbl->buckets[hash];
}
-static inline struct rhash_head __rcu **rht_bucket_insert(
+static inline struct rhash_lock_head __rcu **rht_bucket_insert(
struct rhashtable *ht, struct bucket_table *tbl, unsigned int hash)
{
return unlikely(tbl->nest) ? rht_bucket_nested_insert(ht, tbl, hash) :
@@ -326,7 +374,7 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
* @hash: the hash value / bucket index
*/
#define rht_for_each(pos, tbl, hash) \
- rht_for_each_from(pos, *rht_bucket(tbl, hash), tbl, hash)
+ rht_for_each_from(pos, rht_ptr(*rht_bucket(tbl, hash)), tbl, hash)
/**
* rht_for_each_entry_from - iterate over hash chain from given head
@@ -351,7 +399,7 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
* @member: name of the &struct rhash_head within the hashable struct.
*/
#define rht_for_each_entry(tpos, pos, tbl, hash, member) \
- rht_for_each_entry_from(tpos, pos, *rht_bucket(tbl, hash), \
+ rht_for_each_entry_from(tpos, pos, rht_ptr(*rht_bucket(tbl, hash)), \
tbl, hash, member)
/**
@@ -367,7 +415,8 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
* remove the loop cursor from the list.
*/
#define rht_for_each_entry_safe(tpos, pos, next, tbl, hash, member) \
- for (pos = rht_dereference_bucket(*rht_bucket(tbl, hash), tbl, hash), \
+ for (pos = rht_dereference_bucket(rht_ptr(*rht_bucket(tbl, hash)), \
+ tbl, hash), \
next = !rht_is_a_nulls(pos) ? \
rht_dereference_bucket(pos->next, tbl, hash) : NULL; \
(!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
@@ -402,8 +451,12 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
* the _rcu mutation primitives such as rhashtable_insert() as long as the
* traversal is guarded by rcu_read_lock().
*/
-#define rht_for_each_rcu(pos, tbl, hash) \
- rht_for_each_rcu_from(pos, *rht_bucket(tbl, hash), tbl, hash)
+#define rht_for_each_rcu(pos, tbl, hash) \
+ for (({barrier(); }), \
+ pos = rht_ptr(rht_dereference_bucket_rcu( \
+ *rht_bucket(tbl, hash), tbl, hash)); \
+ !rht_is_a_nulls(pos); \
+ pos = rcu_dereference_raw(pos->next))
/**
* rht_for_each_entry_rcu_from - iterated over rcu hash chain from given head
@@ -437,7 +490,8 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
* traversal is guarded by rcu_read_lock().
*/
#define rht_for_each_entry_rcu(tpos, pos, tbl, hash, member) \
- rht_for_each_entry_rcu_from(tpos, pos, *rht_bucket(tbl, hash), \
+ rht_for_each_entry_rcu_from(tpos, pos, \
+ rht_ptr(*rht_bucket(tbl, hash)), \
tbl, hash, member)
/**
@@ -483,7 +537,7 @@ static inline struct rhash_head *__rhashtable_lookup(
.ht = ht,
.key = key,
};
- struct rhash_head __rcu * const *head;
+ struct rhash_lock_head __rcu * const *bkt;
struct bucket_table *tbl;
struct rhash_head *he;
unsigned int hash;
@@ -491,9 +545,10 @@ static inline struct rhash_head *__rhashtable_lookup(
tbl = rht_dereference_rcu(ht->tbl, ht);
restart:
hash = rht_key_hashfn(ht, tbl, key, params);
- head = rht_bucket(tbl, hash);
+ bkt = rht_bucket(tbl, hash);
do {
- rht_for_each_rcu_from(he, *head, tbl, hash) {
+ he = rht_ptr(rht_dereference_bucket_rcu(*bkt, tbl, hash));
+ rht_for_each_rcu_from(he, he, tbl, hash) {
if (params.obj_cmpfn ?
params.obj_cmpfn(&arg, rht_obj(ht, he)) :
rhashtable_compare(&arg, rht_obj(ht, he)))
@@ -503,7 +558,7 @@ restart:
/* An object might have been moved to a different hash chain,
* while we walk along it - better check and retry.
*/
- } while (he != RHT_NULLS_MARKER(head));
+ } while (he != RHT_NULLS_MARKER(bkt));
/* Ensure we see any new tables. */
smp_rmb();
@@ -599,10 +654,10 @@ static inline void *__rhashtable_insert_fast(
.ht = ht,
.key = key,
};
+ struct rhash_lock_head __rcu **bkt;
struct rhash_head __rcu **pprev;
struct bucket_table *tbl;
struct rhash_head *head;
- spinlock_t *lock;
unsigned int hash;
int elasticity;
void *data;
@@ -611,23 +666,22 @@ static inline void *__rhashtable_insert_fast(
tbl = rht_dereference_rcu(ht->tbl, ht);
hash = rht_head_hashfn(ht, tbl, obj, params);
- lock = rht_bucket_lock(tbl, hash);
- spin_lock_bh(lock);
+ elasticity = RHT_ELASTICITY;
+ bkt = rht_bucket_insert(ht, tbl, hash);
+ data = ERR_PTR(-ENOMEM);
+ if (!bkt)
+ goto out;
+ pprev = NULL;
+ rht_lock(bkt);
if (unlikely(rcu_access_pointer(tbl->future_tbl))) {
slow_path:
- spin_unlock_bh(lock);
+ rht_unlock(bkt);
rcu_read_unlock();
return rhashtable_insert_slow(ht, key, obj);
}
- elasticity = RHT_ELASTICITY;
- pprev = rht_bucket_insert(ht, tbl, hash);
- data = ERR_PTR(-ENOMEM);
- if (!pprev)
- goto out;
-
- rht_for_each_from(head, *pprev, tbl, hash) {
+ rht_for_each_from(head, rht_ptr(*bkt), tbl, hash) {
struct rhlist_head *plist;
struct rhlist_head *list;
@@ -643,7 +697,7 @@ slow_path:
data = rht_obj(ht, head);
if (!rhlist)
- goto out;
+ goto out_unlock;
list = container_of(obj, struct rhlist_head, rhead);
@@ -652,9 +706,13 @@ slow_path:
RCU_INIT_POINTER(list->next, plist);
head = rht_dereference_bucket(head->next, tbl, hash);
RCU_INIT_POINTER(list->rhead.next, head);
- rcu_assign_pointer(*pprev, obj);
-
- goto good;
+ if (pprev) {
+ rcu_assign_pointer(*pprev, obj);
+ rht_unlock(bkt);
+ } else
+ rht_assign_unlock(bkt, obj);
+ data = NULL;
+ goto out;
}
if (elasticity <= 0)
@@ -662,12 +720,13 @@ slow_path:
data = ERR_PTR(-E2BIG);
if (unlikely(rht_grow_above_max(ht, tbl)))
- goto out;
+ goto out_unlock;
if (unlikely(rht_grow_above_100(ht, tbl)))
goto slow_path;
- head = rht_dereference_bucket(*pprev, tbl, hash);
+ /* Inserting at head of list makes unlocking free. */
+ head = rht_ptr(rht_dereference_bucket(*bkt, tbl, hash));
RCU_INIT_POINTER(obj->next, head);
if (rhlist) {
@@ -677,20 +736,21 @@ slow_path:
RCU_INIT_POINTER(list->next, NULL);
}
- rcu_assign_pointer(*pprev, obj);
-
atomic_inc(&ht->nelems);
+ rht_assign_unlock(bkt, obj);
+
if (rht_grow_above_75(ht, tbl))
schedule_work(&ht->run_work);
-good:
data = NULL;
-
out:
- spin_unlock_bh(lock);
rcu_read_unlock();
return data;
+
+out_unlock:
+ rht_unlock(bkt);
+ goto out;
}
/**
@@ -699,9 +759,9 @@ out:
* @obj: pointer to hash head inside object
* @params: hash table parameters
*
- * Will take a per bucket spinlock to protect against mutual mutations
+ * Will take the per bucket bitlock to protect against mutual mutations
* on the same bucket. Multiple insertions may occur in parallel unless
- * they map to the same bucket lock.
+ * they map to the same bucket.
*
* It is safe to call this function from atomic context.
*
@@ -728,9 +788,9 @@ static inline int rhashtable_insert_fast(
* @list: pointer to hash list head inside object
* @params: hash table parameters
*
- * Will take a per bucket spinlock to protect against mutual mutations
+ * Will take the per bucket bitlock to protect against mutual mutations
* on the same bucket. Multiple insertions may occur in parallel unless
- * they map to the same bucket lock.
+ * they map to the same bucket.
*
* It is safe to call this function from atomic context.
*
@@ -751,9 +811,9 @@ static inline int rhltable_insert_key(
* @list: pointer to hash list head inside object
* @params: hash table parameters
*
- * Will take a per bucket spinlock to protect against mutual mutations
+ * Will take the per bucket bitlock to protect against mutual mutations
* on the same bucket. Multiple insertions may occur in parallel unless
- * they map to the same bucket lock.
+ * they map to the same bucket.
*
* It is safe to call this function from atomic context.
*
@@ -880,21 +940,20 @@ static inline int __rhashtable_remove_fast_one(
struct rhash_head *obj, const struct rhashtable_params params,
bool rhlist)
{
+ struct rhash_lock_head __rcu **bkt;
struct rhash_head __rcu **pprev;
struct rhash_head *he;
- spinlock_t * lock;
unsigned int hash;
int err = -ENOENT;
hash = rht_head_hashfn(ht, tbl, obj, params);
- lock = rht_bucket_lock(tbl, hash);
+ bkt = rht_bucket_var(tbl, hash);
+ if (!bkt)
+ return -ENOENT;
+ pprev = NULL;
+ rht_lock(bkt);
- spin_lock_bh(lock);
-
- pprev = rht_bucket_var(tbl, hash);
- if (!pprev)
- goto out;
- rht_for_each_from(he, *pprev, tbl, hash) {
+ rht_for_each_from(he, rht_ptr(*bkt), tbl, hash) {
struct rhlist_head *list;
list = container_of(he, struct rhlist_head, rhead);
@@ -934,13 +993,17 @@ static inline int __rhashtable_remove_fast_one(
}
}
- rcu_assign_pointer(*pprev, obj);
- break;
+ if (pprev) {
+ rcu_assign_pointer(*pprev, obj);
+ rht_unlock(bkt);
+ } else {
+ rht_assign_unlock(bkt, obj);
+ }
+ goto unlocked;
}
-out:
- spin_unlock_bh(lock);
-
+ rht_unlock(bkt);
+unlocked:
if (err > 0) {
atomic_dec(&ht->nelems);
if (unlikely(ht->p.automatic_shrinking &&
@@ -1029,9 +1092,9 @@ static inline int __rhashtable_replace_fast(
struct rhash_head *obj_old, struct rhash_head *obj_new,
const struct rhashtable_params params)
{
+ struct rhash_lock_head __rcu **bkt;
struct rhash_head __rcu **pprev;
struct rhash_head *he;
- spinlock_t *lock;
unsigned int hash;
int err = -ENOENT;
@@ -1042,27 +1105,33 @@ static inline int __rhashtable_replace_fast(
if (hash != rht_head_hashfn(ht, tbl, obj_new, params))
return -EINVAL;
- lock = rht_bucket_lock(tbl, hash);
+ bkt = rht_bucket_var(tbl, hash);
+ if (!bkt)
+ return -ENOENT;
- spin_lock_bh(lock);
+ pprev = NULL;
+ rht_lock(bkt);
- pprev = rht_bucket_var(tbl, hash);
- if (!pprev)
- goto out;
- rht_for_each_from(he, *pprev, tbl, hash) {
+ rht_for_each_from(he, rht_ptr(*bkt), tbl, hash) {
if (he != obj_old) {
pprev = &he->next;
continue;
}
rcu_assign_pointer(obj_new->next, obj_old->next);
- rcu_assign_pointer(*pprev, obj_new);
+ if (pprev) {
+ rcu_assign_pointer(*pprev, obj_new);
+ rht_unlock(bkt);
+ } else {
+ rht_assign_unlock(bkt, obj_new);
+ }
err = 0;
- break;
+ goto unlocked;
}
-out:
- spin_unlock_bh(lock);
+ rht_unlock(bkt);
+
+unlocked:
return err;
}