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Date: Thu, 29 Oct 2020 00:19:25 -0700
From: Song Liu <songliubraving@...com>
To: <netdev@...r.kernel.org>, <bpf@...r.kernel.org>
CC: <kernel-team@...com>, <ast@...nel.org>, <daniel@...earbox.net>,
<john.fastabend@...il.com>, <kpsingh@...omium.org>,
Song Liu <songliubraving@...com>
Subject: [PATCH bpf-next 2/2] bpf: Avoid hashtab deadlock with map_locked
If a hashtab is accessed in both non-NMI and NMI context, the system may
deadlock on bucket->lock. Fix this issue with percpu counter map_locked.
map_locked rejects concurrent access to the same bucket from the same CPU.
To reduce memory overhead, map_locked is not added per bucket. Instead,
8 percpu counters are added to each hashtab. buckets are assigned to these
counters based on the lower bits of its hash.
Signed-off-by: Song Liu <songliubraving@...com>
---
kernel/bpf/hashtab.c | 114 +++++++++++++++++++++++++++++++------------
1 file changed, 82 insertions(+), 32 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 278da031c91ab..da59ba978d172 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -86,6 +86,9 @@ struct bucket {
};
};
+#define HASHTAB_MAP_LOCK_COUNT 8
+#define HASHTAB_MAP_LOCK_MASK (HASHTAB_MAP_LOCK_COUNT - 1)
+
struct bpf_htab {
struct bpf_map map;
struct bucket *buckets;
@@ -100,6 +103,7 @@ struct bpf_htab {
u32 elem_size; /* size of each element in bytes */
u32 hashrnd;
struct lock_class_key lockdep_key;
+ int __percpu *map_locked[HASHTAB_MAP_LOCK_COUNT];
};
/* each htab element is struct htab_elem + key + value */
@@ -152,26 +156,41 @@ static void htab_init_buckets(struct bpf_htab *htab)
}
}
-static inline unsigned long htab_lock_bucket(const struct bpf_htab *htab,
- struct bucket *b)
+static inline int htab_lock_bucket(const struct bpf_htab *htab,
+ struct bucket *b, u32 hash,
+ unsigned long *pflags)
{
unsigned long flags;
+ hash = hash & HASHTAB_MAP_LOCK_MASK;
+
+ migrate_disable();
+ if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
+ __this_cpu_dec(*(htab->map_locked[hash]));
+ migrate_enable();
+ return -EBUSY;
+ }
+
if (htab_use_raw_lock(htab))
raw_spin_lock_irqsave(&b->raw_lock, flags);
else
spin_lock_irqsave(&b->lock, flags);
- return flags;
+ *pflags = flags;
+
+ return 0;
}
static inline void htab_unlock_bucket(const struct bpf_htab *htab,
- struct bucket *b,
+ struct bucket *b, u32 hash,
unsigned long flags)
{
+ hash = hash & HASHTAB_MAP_LOCK_MASK;
if (htab_use_raw_lock(htab))
raw_spin_unlock_irqrestore(&b->raw_lock, flags);
else
spin_unlock_irqrestore(&b->lock, flags);
+ __this_cpu_dec(*(htab->map_locked[hash]));
+ migrate_enable();
}
static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node);
@@ -429,8 +448,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
bool percpu_lru = (attr->map_flags & BPF_F_NO_COMMON_LRU);
bool prealloc = !(attr->map_flags & BPF_F_NO_PREALLOC);
struct bpf_htab *htab;
+ int err, i;
u64 cost;
- int err;
htab = kzalloc(sizeof(*htab), GFP_USER);
if (!htab)
@@ -487,6 +506,13 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
if (!htab->buckets)
goto free_charge;
+ for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++) {
+ htab->map_locked[i] = __alloc_percpu_gfp(sizeof(int),
+ sizeof(int), GFP_USER);
+ if (!htab->map_locked[i])
+ goto free_map_locked;
+ }
+
if (htab->map.map_flags & BPF_F_ZERO_SEED)
htab->hashrnd = 0;
else
@@ -497,7 +523,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
if (prealloc) {
err = prealloc_init(htab);
if (err)
- goto free_buckets;
+ goto free_map_locked;
if (!percpu && !lru) {
/* lru itself can remove the least used element, so
@@ -513,7 +539,9 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
free_prealloc:
prealloc_destroy(htab);
-free_buckets:
+free_map_locked:
+ for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
+ free_percpu(htab->map_locked[i]);
bpf_map_area_free(htab->buckets);
free_charge:
bpf_map_charge_finish(&htab->map.memory);
@@ -694,12 +722,15 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
struct hlist_nulls_node *n;
unsigned long flags;
struct bucket *b;
+ int ret;
tgt_l = container_of(node, struct htab_elem, lru_node);
b = __select_bucket(htab, tgt_l->hash);
head = &b->head;
- flags = htab_lock_bucket(htab, b);
+ ret = htab_lock_bucket(htab, b, tgt_l->hash, &flags);
+ if (ret)
+ return false;
hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
if (l == tgt_l) {
@@ -707,7 +738,7 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
break;
}
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, tgt_l->hash, flags);
return l == tgt_l;
}
@@ -979,7 +1010,9 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
*/
}
- flags = htab_lock_bucket(htab, b);
+ ret = htab_lock_bucket(htab, b, hash, &flags);
+ if (ret)
+ return ret;
l_old = lookup_elem_raw(head, hash, key, key_size);
@@ -1020,7 +1053,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
}
ret = 0;
err:
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, hash, flags);
return ret;
}
@@ -1058,7 +1091,9 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
return -ENOMEM;
memcpy(l_new->key + round_up(map->key_size, 8), value, map->value_size);
- flags = htab_lock_bucket(htab, b);
+ ret = htab_lock_bucket(htab, b, hash, &flags);
+ if (ret)
+ return ret;
l_old = lookup_elem_raw(head, hash, key, key_size);
@@ -1077,7 +1112,7 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
ret = 0;
err:
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, hash, flags);
if (ret)
bpf_lru_push_free(&htab->lru, &l_new->lru_node);
@@ -1112,7 +1147,9 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
b = __select_bucket(htab, hash);
head = &b->head;
- flags = htab_lock_bucket(htab, b);
+ ret = htab_lock_bucket(htab, b, hash, &flags);
+ if (ret)
+ return ret;
l_old = lookup_elem_raw(head, hash, key, key_size);
@@ -1135,7 +1172,7 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
}
ret = 0;
err:
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, hash, flags);
return ret;
}
@@ -1175,7 +1212,9 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
return -ENOMEM;
}
- flags = htab_lock_bucket(htab, b);
+ ret = htab_lock_bucket(htab, b, hash, &flags);
+ if (ret)
+ return ret;
l_old = lookup_elem_raw(head, hash, key, key_size);
@@ -1197,7 +1236,7 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
}
ret = 0;
err:
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, hash, flags);
if (l_new)
bpf_lru_push_free(&htab->lru, &l_new->lru_node);
return ret;
@@ -1225,7 +1264,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
struct htab_elem *l;
unsigned long flags;
u32 hash, key_size;
- int ret = -ENOENT;
+ int ret;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
@@ -1235,17 +1274,20 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
b = __select_bucket(htab, hash);
head = &b->head;
- flags = htab_lock_bucket(htab, b);
+ ret = htab_lock_bucket(htab, b, hash, &flags);
+ if (ret)
+ return ret;
l = lookup_elem_raw(head, hash, key, key_size);
if (l) {
hlist_nulls_del_rcu(&l->hash_node);
free_htab_elem(htab, l);
- ret = 0;
+ } else {
+ ret = -ENOENT;
}
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, hash, flags);
return ret;
}
@@ -1257,7 +1299,7 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key)
struct htab_elem *l;
unsigned long flags;
u32 hash, key_size;
- int ret = -ENOENT;
+ int ret;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
@@ -1267,16 +1309,18 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key)
b = __select_bucket(htab, hash);
head = &b->head;
- flags = htab_lock_bucket(htab, b);
+ ret = htab_lock_bucket(htab, b, hash, &flags);
+ if (ret)
+ return ret;
l = lookup_elem_raw(head, hash, key, key_size);
- if (l) {
+ if (l)
hlist_nulls_del_rcu(&l->hash_node);
- ret = 0;
- }
+ else
+ ret = -ENOENT;
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, hash, flags);
if (l)
bpf_lru_push_free(&htab->lru, &l->lru_node);
return ret;
@@ -1302,6 +1346,7 @@ static void delete_all_elements(struct bpf_htab *htab)
static void htab_map_free(struct bpf_map *map)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
+ int i;
/* bpf_free_used_maps() or close(map_fd) will trigger this map_free callback.
* bpf_free_used_maps() is called after bpf prog is no longer executing.
@@ -1320,6 +1365,8 @@ static void htab_map_free(struct bpf_map *map)
free_percpu(htab->extra_elems);
bpf_map_area_free(htab->buckets);
lockdep_unregister_key(&htab->lockdep_key);
+ for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
+ free_percpu(htab->map_locked[i]);
kfree(htab);
}
@@ -1423,8 +1470,11 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
b = &htab->buckets[batch];
head = &b->head;
/* do not grab the lock unless need it (bucket_cnt > 0). */
- if (locked)
- flags = htab_lock_bucket(htab, b);
+ if (locked) {
+ ret = htab_lock_bucket(htab, b, batch, &flags);
+ if (ret)
+ goto next_batch;
+ }
bucket_cnt = 0;
hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
@@ -1441,7 +1491,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
/* Note that since bucket_cnt > 0 here, it is implicit
* that the locked was grabbed, so release it.
*/
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, batch, flags);
rcu_read_unlock();
bpf_enable_instrumentation();
goto after_loop;
@@ -1452,7 +1502,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
/* Note that since bucket_cnt > 0 here, it is implicit
* that the locked was grabbed, so release it.
*/
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, batch, flags);
rcu_read_unlock();
bpf_enable_instrumentation();
kvfree(keys);
@@ -1505,7 +1555,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
dst_val += value_size;
}
- htab_unlock_bucket(htab, b, flags);
+ htab_unlock_bucket(htab, b, batch, flags);
locked = false;
while (node_to_free) {
--
2.24.1
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