bpf: hash: use per-bucket spinlock

Both htab_map_update_elem() and htab_map_delete_elem() can be
called from eBPF program, and they may be in kernel hot path,
so it isn't efficient to use a per-hashtable lock in this two
helpers.

The per-hashtable spinlock is used for protecting bucket's
hlist, and per-bucket lock is just enough. This patch converts
the per-hashtable lock into per-bucket spinlock, so that
contention can be decreased a lot.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index d857fcb3607b6b958d9b7c9f71a148ebadd1425d..c5b30fd8a3151f99b8cf175ad2a7ce563a0e13c8 100644 (file)
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -14,10 +14,14 @@
 #include <linux/filter.h>
 #include <linux/vmalloc.h>
 
+struct bucket {
+       struct hlist_head head;
+       raw_spinlock_t lock;
+};
+
 struct bpf_htab {
        struct bpf_map map;
-       struct hlist_head *buckets;
-       raw_spinlock_t lock;
+       struct bucket *buckets;
        atomic_t count; /* number of elements in this hashtable */
        u32 n_buckets;  /* number of hash buckets */
        u32 elem_size;  /* size of each element in bytes */
@@ -79,33 +83,34 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 
        /* prevent zero size kmalloc and check for u32 overflow */
        if (htab->n_buckets == 0 ||
-           htab->n_buckets > U32_MAX / sizeof(struct hlist_head))
+           htab->n_buckets > U32_MAX / sizeof(struct bucket))
                goto free_htab;
 
-       if ((u64) htab->n_buckets * sizeof(struct hlist_head) +
+       if ((u64) htab->n_buckets * sizeof(struct bucket) +
            (u64) htab->elem_size * htab->map.max_entries >=
            U32_MAX - PAGE_SIZE)
                /* make sure page count doesn't overflow */
                goto free_htab;
 
-       htab->map.pages = round_up(htab->n_buckets * sizeof(struct hlist_head) +
+       htab->map.pages = round_up(htab->n_buckets * sizeof(struct bucket) +
                                   htab->elem_size * htab->map.max_entries,
                                   PAGE_SIZE) >> PAGE_SHIFT;
 
        err = -ENOMEM;
-       htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct hlist_head),
+       htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct bucket),
                                      GFP_USER | __GFP_NOWARN);
 
        if (!htab->buckets) {
-               htab->buckets = vmalloc(htab->n_buckets * sizeof(struct hlist_head));
+               htab->buckets = vmalloc(htab->n_buckets * sizeof(struct bucket));
                if (!htab->buckets)
                        goto free_htab;
        }
 
-       for (i = 0; i < htab->n_buckets; i++)
-               INIT_HLIST_HEAD(&htab->buckets[i]);
+       for (i = 0; i < htab->n_buckets; i++) {
+               INIT_HLIST_HEAD(&htab->buckets[i].head);
+               raw_spin_lock_init(&htab->buckets[i].lock);
+       }
 
-       raw_spin_lock_init(&htab->lock);
        atomic_set(&htab->count, 0);
 
        return &htab->map;
@@ -120,11 +125,16 @@ static inline u32 htab_map_hash(const void *key, u32 key_len)
        return jhash(key, key_len, 0);
 }
 
-static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
+static inline struct bucket *__select_bucket(struct bpf_htab *htab, u32 hash)
 {
        return &htab->buckets[hash & (htab->n_buckets - 1)];
 }
 
+static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
+{
+       return &__select_bucket(htab, hash)->head;
+}
+
 static struct htab_elem *lookup_elem_raw(struct hlist_head *head, u32 hash,
                                         void *key, u32 key_size)
 {
@@ -227,6 +237,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
        struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
        struct htab_elem *l_new, *l_old;
        struct hlist_head *head;
+       struct bucket *b;
        unsigned long flags;
        u32 key_size;
        int ret;
@@ -248,10 +259,11 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
        memcpy(l_new->key + round_up(key_size, 8), value, map->value_size);
 
        l_new->hash = htab_map_hash(l_new->key, key_size);
-       head = select_bucket(htab, l_new->hash);
+       b = __select_bucket(htab, l_new->hash);
+       head = &b->head;
 
        /* bpf_map_update_elem() can be called in_irq() */
-       raw_spin_lock_irqsave(&htab->lock, flags);
+       raw_spin_lock_irqsave(&b->lock, flags);
 
        l_old = lookup_elem_raw(head, l_new->hash, key, key_size);
 
@@ -285,11 +297,11 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
        } else {
                atomic_inc(&htab->count);
        }
-       raw_spin_unlock_irqrestore(&htab->lock, flags);
+       raw_spin_unlock_irqrestore(&b->lock, flags);
 
        return 0;
 err:
-       raw_spin_unlock_irqrestore(&htab->lock, flags);
+       raw_spin_unlock_irqrestore(&b->lock, flags);
        kfree(l_new);
        return ret;
 }
@@ -299,6 +311,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
 {
        struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
        struct hlist_head *head;
+       struct bucket *b;
        struct htab_elem *l;
        unsigned long flags;
        u32 hash, key_size;
@@ -309,9 +322,10 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
        key_size = map->key_size;
 
        hash = htab_map_hash(key, key_size);
-       head = select_bucket(htab, hash);
+       b = __select_bucket(htab, hash);
+       head = &b->head;
 
-       raw_spin_lock_irqsave(&htab->lock, flags);
+       raw_spin_lock_irqsave(&b->lock, flags);
 
        l = lookup_elem_raw(head, hash, key, key_size);
 
@@ -322,7 +336,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
                ret = 0;
        }
 
-       raw_spin_unlock_irqrestore(&htab->lock, flags);
+       raw_spin_unlock_irqrestore(&b->lock, flags);
        return ret;
 }