On 04/10/2019 07:08 PM, Yonghong Song wrote:
> On 4/10/19 7:30 AM, Sebastian Andrzej Siewior wrote:
>> There is no difference between spinlock_t and raw_spinlock_t for !RT
>> kernels. It is possible that bpf_lru_list_pop_free_to_local() invokes
>> at least three list walks which look unbounded it probably makes sense
>> to use spinlock_t.
>>
>> Make bpf_lru_list use a spinlock_t.
>
> Could you add a cover letter for the patch set since you have
> more than one patch?
>
>> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
>> ---
>> kernel/bpf/bpf_lru_list.c | 38 +++++++++++++++++++-------------------
>> kernel/bpf/bpf_lru_list.h | 4 ++--
>> 2 files changed, 21 insertions(+), 21 deletions(-)
>>
>> diff --git a/kernel/bpf/bpf_lru_list.c b/kernel/bpf/bpf_lru_list.c
>> index e6ef4401a1380..40f47210c3817 100644
>> --- a/kernel/bpf/bpf_lru_list.c
>> +++ b/kernel/bpf/bpf_lru_list.c
>> @@ -313,9 +313,9 @@ static void bpf_lru_list_push_free(struct bpf_lru_list *l,
>> if (WARN_ON_ONCE(IS_LOCAL_LIST_TYPE(node->type)))
>> return;
>>
>> - raw_spin_lock_irqsave(&l->lock, flags);
>> + spin_lock_irqsave(&l->lock, flags);
>> __bpf_lru_node_move(l, node, BPF_LRU_LIST_T_FREE);
>> - raw_spin_unlock_irqrestore(&l->lock, flags);
>> + spin_unlock_irqrestore(&l->lock, flags);
>> }
>
> This function (plus many others) is called by bpf program helpers which
> cannot sleep. Is it possible that under RT spin_lock_irqsave() could
> sleep and this will make bpf subsystem cannot be used under RT?
Back then in ac00881f9221 ("bpf: convert hashtab lock to raw lock")
Yang Shi converted spinlock_t to raw_spinlock_t due to exactly the
above mentioned issue. I presume that hasn't changed, right?
>> static void bpf_lru_list_pop_free_to_local(struct bpf_lru *lru,
>> @@ -325,7 +325,7 @@ static void bpf_lru_list_pop_free_to_local(struct bpf_lru *lru,
>> struct bpf_lru_node *node, *tmp_node;
>> unsigned int nfree = 0;
>>
>> - raw_spin_lock(&l->lock);
>> + spin_lock(&l->lock);
>>
>> __local_list_flush(l, loc_l);
>>
>> @@ -344,7 +344,7 @@ static void bpf_lru_list_pop_free_to_local(struct bpf_lru *lru,
>> local_free_list(loc_l),
>> BPF_LRU_LOCAL_LIST_T_FREE);
>>
>> - raw_spin_unlock(&l->lock);
>> + spin_unlock(&l->lock);
>> }
>>
>> static void __local_list_add_pending(struct bpf_lru *lru,
> [...]
>> static void bpf_lru_list_init(struct bpf_lru_list *l)
>> @@ -642,7 +642,7 @@ static void bpf_lru_list_init(struct bpf_lru_list *l)
>>
>> l->next_inactive_rotation = &l->lists[BPF_LRU_LIST_T_INACTIVE];
>>
>> - raw_spin_lock_init(&l->lock);
>> + spin_lock_init(&l->lock);
>> }
>>
>> int bpf_lru_init(struct bpf_lru *lru, bool percpu, u32 hash_offset,
>> diff --git a/kernel/bpf/bpf_lru_list.h b/kernel/bpf/bpf_lru_list.h
>> index 7d4f89b7cb841..4e1e4608f1bb0 100644
>> --- a/kernel/bpf/bpf_lru_list.h
>> +++ b/kernel/bpf/bpf_lru_list.h
>> @@ -36,13 +36,13 @@ struct bpf_lru_list {
>> /* The next inacitve list rotation starts from here */
>> struct list_head *next_inactive_rotation;
>>
>> - raw_spinlock_t lock ____cacheline_aligned_in_smp;
>> + spinlock_t lock ____cacheline_aligned_in_smp;
>> };
>>
>> struct bpf_lru_locallist {
>> struct list_head lists[NR_BPF_LRU_LOCAL_LIST_T];
>> u16 next_steal;
>> - raw_spinlock_t lock;
>> + spinlock_t lock;
>> };
>>
>> struct bpf_common_lru {
>>
