[Devel] [PATCH vz9 v1 06/63] dm-ploop: convert enospc handling to use lockless lists

[Pavel Tikhomirov]

On 2/3/25 14:45, Alexander Atanasov wrote:
> On 3.02.25 8:01, Pavel Tikhomirov wrote:
>>
>>> @@ -166,7 +171,6 @@ static bool ploop_try_delay_enospc(struct 
>>> ploop_rq *prq, struct pio *pio)
>>>       bool delayed = true;
>>>       unsigned long flags;
>>> -    spin_lock_irqsave(&ploop->deferred_lock, flags);
>>>       if (unlikely(ploop->wants_suspend)) {
>>>           delayed = false;
>>>           goto unlock;
>>> @@ -176,10 +180,11 @@ static bool ploop_try_delay_enospc(struct 
>>> ploop_rq *prq, struct pio *pio)
>>>       pr_err_once(PL_FMT("underlying disk is almost full"),
>>>           ploop_device_name(ploop));
>>> +    spin_lock_irqsave(&ploop->deferred_lock, flags);
>>>       ploop->event_enospc = true;
>>> -    list_add_tail(&pio->list, &ploop->enospc_pios);
>>> -unlock:
>>>       spin_unlock_irqrestore(&ploop->deferred_lock, flags);
>>> +    llist_add((struct llist_node *)(&pio->list), &ploop->enospc_pios);
>>> +unlock:
>>>       if (delayed)
>>>           mod_timer(&ploop->enospc_timer, jiffies + 
>>> PLOOP_ENOSPC_TIMEOUT);
>>
>> Can you please explain why we need to take defered_lock around ploop- 
>> >event_enospc setting after your patch? (It looks that this lock does 
>> not do anything now.)
>>
> 
> see static int ploop_get_event(...), without lock event can be missed

That is not an explanation. How exactly can it be missed?

> 

-- 
Best regards, Tikhomirov Pavel
Senior Software Developer, Virtuozzo.