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Message-ID: <41eda0ea-0ed4-1ffb-5520-06fda08e5d38@huawei.com>
Date: Tue, 22 Nov 2022 12:06:28 +0800
From: Hou Tao <houtao1@...wei.com>
To: Tonghao Zhang <xiangxia.m.yue@...il.com>
CC: <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
bpf <bpf@...r.kernel.org>
Subject: Re: [net-next] bpf: avoid hashtab deadlock with try_lock
Hi,
On 11/22/2022 12:01 PM, Hou Tao wrote:
> Hi,
>
> On 11/22/2022 11:12 AM, Tonghao Zhang wrote:
>> .
>>
>> On Tue, Nov 22, 2022 at 9:16 AM Hou Tao <houtao1@...wei.com> wrote:
>>> Hi,
>>>
>>> On 11/21/2022 6:05 PM, xiangxia.m.yue@...il.com wrote:
>>>> From: Tonghao Zhang <xiangxia.m.yue@...il.com>
>>>>
>>>> The commit 20b6cc34ea74 ("bpf: Avoid hashtab deadlock with map_locked"),
>>>> try to fix deadlock, but in some case, the deadlock occurs:
>>>>
>>>> * CPUn in task context with K1, and taking lock.
>>>> * CPUn interrupted by NMI context, with K2.
>>>> * They are using the same bucket, but different map_locked.
>>> It is possible when n_buckets is less than HASHTAB_MAP_LOCK_COUNT (e.g.,
>>> n_bucket=4). If using hash & min(HASHTAB_MAP_LOCK_MASK, n_bucket - 1) as the
>>> index of map_locked, I think the deadlock will be gone.
>> Yes, but for saving memory, HASHTAB_MAP_LOCK_MASK should not be too
>> large(now this value is 8-1).
>> if user define n_bucket ,e.g 8192, the part of bucket only are
>> selected via hash & min(HASHTAB_MAP_LOCK_MASK, n_bucket - 1).
I don't mean to extend map_locked. Using hash & min(HASHTAB_MAP_LOCK_MASK,
n_bucket - 1) as index of map_locked can guarantee the same map_locked will be
used if different update processes are using the same bucket lock.
> SNIP
>>>> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
>>>> index 22855d6ff6d3..429acd97c869 100644
>>>> --- a/kernel/bpf/hashtab.c
>>>> +++ b/kernel/bpf/hashtab.c
>>>> @@ -80,9 +80,6 @@ struct bucket {
>>>> raw_spinlock_t raw_lock;
>>>> };
>>>>
>>>> -#define HASHTAB_MAP_LOCK_COUNT 8
>>>> -#define HASHTAB_MAP_LOCK_MASK (HASHTAB_MAP_LOCK_COUNT - 1)
>>>> -
>>>> struct bpf_htab {
>>>> struct bpf_map map;
>>>> struct bpf_mem_alloc ma;
>>>> @@ -104,7 +101,6 @@ 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 */
>>>> @@ -146,35 +142,26 @@ static void htab_init_buckets(struct bpf_htab *htab)
>>>> }
>>>> }
>>>>
>>>> -static inline int htab_lock_bucket(const struct bpf_htab *htab,
>>>> - struct bucket *b, u32 hash,
>>>> +static inline int htab_lock_bucket(struct bucket *b,
>>>> unsigned long *pflags)
>>>> {
>>>> unsigned long flags;
>>>>
>>>> - hash = hash & HASHTAB_MAP_LOCK_MASK;
>>>> -
>>>> - preempt_disable();
>>>> - if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
>>>> - __this_cpu_dec(*(htab->map_locked[hash]));
>>>> - preempt_enable();
>>>> - return -EBUSY;
>>>> + if (in_nmi()) {
>>>> + if (!raw_spin_trylock_irqsave(&b->raw_lock, flags))
>>>> + return -EBUSY;
>>>> + } else {
>>>> + raw_spin_lock_irqsave(&b->raw_lock, flags);
>>>> }
>>>>
>>>> - raw_spin_lock_irqsave(&b->raw_lock, flags);
>>>> *pflags = flags;
>>>> -
>>>> return 0;
>>>> }
>>> map_locked is also used to prevent the re-entrance of htab_lock_bucket() on the
>>> same CPU, so only check in_nmi() is not enough.
>> NMI, IRQ, and preempt may interrupt the task context.
>> In htab_lock_bucket, raw_spin_lock_irqsave disable the preempt and
>> irq. so only NMI may interrupt the codes, right ?
> The re-entrance here means the nesting of bpf programs as show below:
>
> bpf_prog A
> update map X
> htab_lock_bucket
> raw_spin_lock_irqsave()
> lookup_elem_raw()
> // bpf prog B is attached on lookup_elem_raw()
> bpf prog B
> update map X again and update the element
> htab_lock_bucket()
> // dead-lock
> raw_spinlock_irqsave()
> .
>
>>>> -static inline void htab_unlock_bucket(const struct bpf_htab *htab,
>>>> - struct bucket *b, u32 hash,
>>>> +static inline void htab_unlock_bucket(struct bucket *b,
>>>> unsigned long flags)
>>>> {
>>>> - hash = hash & HASHTAB_MAP_LOCK_MASK;
>>>> raw_spin_unlock_irqrestore(&b->raw_lock, flags);
>>>> - __this_cpu_dec(*(htab->map_locked[hash]));
>>>> - preempt_enable();
>>>> }
>>>>
>>>> static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node);
>>>> @@ -467,7 +454,7 @@ 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;
>>>> + int err;
>>>>
>>>> htab = bpf_map_area_alloc(sizeof(*htab), NUMA_NO_NODE);
>>>> if (!htab)
>>>> @@ -513,15 +500,6 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
>>>> if (!htab->buckets)
>>>> goto free_htab;
>>>>
>>>> - for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++) {
>>>> - htab->map_locked[i] = bpf_map_alloc_percpu(&htab->map,
>>>> - 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
>>>> @@ -549,13 +527,13 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
>>>> if (htab->use_percpu_counter) {
>>>> err = percpu_counter_init(&htab->pcount, 0, GFP_KERNEL);
>>>> if (err)
>>>> - goto free_map_locked;
>>>> + goto free_buckets;
>>>> }
>>>>
>>>> if (prealloc) {
>>>> err = prealloc_init(htab);
>>>> if (err)
>>>> - goto free_map_locked;
>>>> + goto free_buckets;
>>>>
>>>> if (!percpu && !lru) {
>>>> /* lru itself can remove the least used element, so
>>>> @@ -568,12 +546,12 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
>>>> } else {
>>>> err = bpf_mem_alloc_init(&htab->ma, htab->elem_size, false);
>>>> if (err)
>>>> - goto free_map_locked;
>>>> + goto free_buckets;
>>>> if (percpu) {
>>>> err = bpf_mem_alloc_init(&htab->pcpu_ma,
>>>> round_up(htab->map.value_size, 8), true);
>>>> if (err)
>>>> - goto free_map_locked;
>>>> + goto free_buckets;
>>>> }
>>>> }
>>>>
>>>> @@ -581,11 +559,10 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
>>>>
>>>> free_prealloc:
>>>> prealloc_destroy(htab);
>>>> -free_map_locked:
>>>> +free_buckets:
>>>> if (htab->use_percpu_counter)
>>>> percpu_counter_destroy(&htab->pcount);
>>>> - for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
>>>> - free_percpu(htab->map_locked[i]);
>>>> +
>>>> bpf_map_area_free(htab->buckets);
>>>> bpf_mem_alloc_destroy(&htab->pcpu_ma);
>>>> bpf_mem_alloc_destroy(&htab->ma);
>>>> @@ -782,7 +759,7 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
>>>> b = __select_bucket(htab, tgt_l->hash);
>>>> head = &b->head;
>>>>
>>>> - ret = htab_lock_bucket(htab, b, tgt_l->hash, &flags);
>>>> + ret = htab_lock_bucket(b, &flags);
>>>> if (ret)
>>>> return false;
>>>>
>>>> @@ -793,7 +770,7 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
>>>> break;
>>>> }
>>>>
>>>> - htab_unlock_bucket(htab, b, tgt_l->hash, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>>
>>>> return l == tgt_l;
>>>> }
>>>> @@ -1107,7 +1084,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
>>>> */
>>>> }
>>>>
>>>> - ret = htab_lock_bucket(htab, b, hash, &flags);
>>>> + ret = htab_lock_bucket(b, &flags);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> @@ -1152,7 +1129,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
>>>> }
>>>> ret = 0;
>>>> err:
>>>> - htab_unlock_bucket(htab, b, hash, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>> return ret;
>>>> }
>>>>
>>>> @@ -1198,7 +1175,7 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
>>>> copy_map_value(&htab->map,
>>>> l_new->key + round_up(map->key_size, 8), value);
>>>>
>>>> - ret = htab_lock_bucket(htab, b, hash, &flags);
>>>> + ret = htab_lock_bucket(b, &flags);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> @@ -1219,7 +1196,7 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
>>>> ret = 0;
>>>>
>>>> err:
>>>> - htab_unlock_bucket(htab, b, hash, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>>
>>>> if (ret)
>>>> htab_lru_push_free(htab, l_new);
>>>> @@ -1255,7 +1232,7 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
>>>> b = __select_bucket(htab, hash);
>>>> head = &b->head;
>>>>
>>>> - ret = htab_lock_bucket(htab, b, hash, &flags);
>>>> + ret = htab_lock_bucket(b, &flags);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> @@ -1280,7 +1257,7 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
>>>> }
>>>> ret = 0;
>>>> err:
>>>> - htab_unlock_bucket(htab, b, hash, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>> return ret;
>>>> }
>>>>
>>>> @@ -1321,7 +1298,7 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
>>>> return -ENOMEM;
>>>> }
>>>>
>>>> - ret = htab_lock_bucket(htab, b, hash, &flags);
>>>> + ret = htab_lock_bucket(b, &flags);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> @@ -1345,7 +1322,7 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
>>>> }
>>>> ret = 0;
>>>> err:
>>>> - htab_unlock_bucket(htab, b, hash, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>> if (l_new)
>>>> bpf_lru_push_free(&htab->lru, &l_new->lru_node);
>>>> return ret;
>>>> @@ -1384,7 +1361,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
>>>> b = __select_bucket(htab, hash);
>>>> head = &b->head;
>>>>
>>>> - ret = htab_lock_bucket(htab, b, hash, &flags);
>>>> + ret = htab_lock_bucket(b, &flags);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> @@ -1397,7 +1374,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
>>>> ret = -ENOENT;
>>>> }
>>>>
>>>> - htab_unlock_bucket(htab, b, hash, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>> return ret;
>>>> }
>>>>
>>>> @@ -1420,7 +1397,7 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key)
>>>> b = __select_bucket(htab, hash);
>>>> head = &b->head;
>>>>
>>>> - ret = htab_lock_bucket(htab, b, hash, &flags);
>>>> + ret = htab_lock_bucket(b, &flags);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> @@ -1431,7 +1408,7 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key)
>>>> else
>>>> ret = -ENOENT;
>>>>
>>>> - htab_unlock_bucket(htab, b, hash, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>> if (l)
>>>> htab_lru_push_free(htab, l);
>>>> return ret;
>>>> @@ -1494,7 +1471,6 @@ static void htab_map_free_timers(struct bpf_map *map)
>>>> 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.
>>>> @@ -1517,10 +1493,10 @@ static void htab_map_free(struct bpf_map *map)
>>>> bpf_map_area_free(htab->buckets);
>>>> bpf_mem_alloc_destroy(&htab->pcpu_ma);
>>>> bpf_mem_alloc_destroy(&htab->ma);
>>>> +
>>>> if (htab->use_percpu_counter)
>>>> percpu_counter_destroy(&htab->pcount);
>>>> - for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
>>>> - free_percpu(htab->map_locked[i]);
>>>> +
>>>> lockdep_unregister_key(&htab->lockdep_key);
>>>> bpf_map_area_free(htab);
>>>> }
>>>> @@ -1564,7 +1540,7 @@ static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
>>>> b = __select_bucket(htab, hash);
>>>> head = &b->head;
>>>>
>>>> - ret = htab_lock_bucket(htab, b, hash, &bflags);
>>>> + ret = htab_lock_bucket(b, &bflags);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> @@ -1602,7 +1578,7 @@ static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
>>>> free_htab_elem(htab, l);
>>>> }
>>>>
>>>> - htab_unlock_bucket(htab, b, hash, bflags);
>>>> + htab_unlock_bucket(b, bflags);
>>>>
>>>> if (is_lru_map && l)
>>>> htab_lru_push_free(htab, l);
>>>> @@ -1720,7 +1696,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
>>>> head = &b->head;
>>>> /* do not grab the lock unless need it (bucket_cnt > 0). */
>>>> if (locked) {
>>>> - ret = htab_lock_bucket(htab, b, batch, &flags);
>>>> + ret = htab_lock_bucket(b, &flags);
>>>> if (ret) {
>>>> rcu_read_unlock();
>>>> bpf_enable_instrumentation();
>>>> @@ -1743,7 +1719,7 @@ __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, batch, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>> rcu_read_unlock();
>>>> bpf_enable_instrumentation();
>>>> goto after_loop;
>>>> @@ -1754,7 +1730,7 @@ __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, batch, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>> rcu_read_unlock();
>>>> bpf_enable_instrumentation();
>>>> kvfree(keys);
>>>> @@ -1815,7 +1791,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
>>>> dst_val += value_size;
>>>> }
>>>>
>>>> - htab_unlock_bucket(htab, b, batch, flags);
>>>> + htab_unlock_bucket(b, flags);
>>>> locked = false;
>>>>
>>>> while (node_to_free) {
> .
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