Re: [dpdk-dev] [PATCH v2] timer: fix resource leak in finalize

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 07-May-19 11:04 PM, Carrillo, Erik G wrote:
> Hi Anatoly,
> 
> Thanks for the review.  Comments in-line:
> 
> <...snipped...>
> 
>>>    #define RTE_MAX_DATA_ELS 64
>>> +static const struct rte_memzone *rte_timer_data_mz; static
>>> +rte_atomic16_t *rte_timer_mz_refcnt;
>>>    static struct rte_timer_data *rte_timer_data_arr;
>>>    static const uint32_t default_data_id;
>>>    static uint32_t rte_timer_subsystem_initialized; @@ -155,6 +157,7 @@
>>> rte_timer_subsystem_init_v1905(void)
>>>    	struct rte_timer_data *data;
>>>    	int i, lcore_id;
>>>    	static const char *mz_name = "rte_timer_mz";
>>> +	size_t data_arr_size = RTE_MAX_DATA_ELS *
>>> +sizeof(*rte_timer_data_arr);
>>
>> nitpicking, but... const?
>>
> 
> No problem - I'll make this change if this line persists into the next version.
> 
> <...snipped...>
> 
>>>
>>> @@ -205,8 +216,11 @@
>> BIND_DEFAULT_SYMBOL(rte_timer_subsystem_init, _v1905, 19.05);
>>>    void __rte_experimental
>>>    rte_timer_subsystem_finalize(void)
>>>    {
>>> -	if (rte_timer_data_arr)
>>> -		rte_free(rte_timer_data_arr);
>>> +	if (!rte_timer_subsystem_initialized)
>>> +		return;
>>> +
>>> +	if (rte_atomic16_dec_and_test(rte_timer_mz_refcnt))
>>> +		rte_memzone_free(rte_timer_data_mz);
>>
>> I think there's a race here. You may get preempted after test but before
>> free, where another secondary could initialize. As far as i know, we also
> 
> Indeed, thanks for catching this.
> 
>> support a case when secondary initializes after primary stops running.
>>
>> Let's even suppose that we allow secondary processes to initialize the timer
>> subsystem by reserving memzone and checking rte_errno. You would still
>> have a chance of two init/deinit conflicting, because there's a hole between
>> memzone allocation and atomic increment.
>>
>> I don't think this race can be resolved in a safe way, so we might just have to
>> settle for a memory leak.
>>
> 
> I don't see a solution here currently either.  I'll look at removing the memzone_free()
> call and possibly the rte_timer_subsystem_finalize() API, since it seems like
> there's no reason for it to exist if it can't free the allocations.

I wonder if there are other places in DPDK where this pattern is used.

Technically, this kind of thing /could/ be resolved by having something 
in our multiprocess shared memory outside of DPDK heap. I.e. store 
something in rte_eal_memconfig like some other things do. This change, 
however, would require an ABI break, so while changing this particular 
API won't need a deprecation notice, the change itself would.

> 
> Regards,
> Erik
> 
>>>
>>>    	rte_timer_subsystem_initialized = 0;
>>>    }
>>>
>>
>>
>> --
>> Thanks,
>> Anatoly


-- 
Thanks,
Anatoly