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

["Carrillo, Erik G" <erik.g.carrillo@intel.com>]

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.

Regards,
Erik

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