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

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

> -----Original Message-----
> From: Burakov, Anatoly
> Sent: Wednesday, May 8, 2019 3:50 AM
> To: Carrillo, Erik G <erik.g.carrillo@intel.com>; rsanford@akamai.com;
> thomas@monjalon.net
> Cc: dev@dpdk.org
> Subject: Re: [PATCH v2] timer: fix resource leak in finalize
> 
> 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.

I like this idea; thanks for the suggestion.  I went ahead and submitted a new version 
of this patch with this approach.  It's dependent on one other new patch that allows
secondary processes to reserve the memzone.  I also submitted a deprecation
notice for the ABI break for the change to rte_mem_config.

Thomas, I suspect that I should mark v3 of this patch as "deferred", so I've gone ahead and
done that, but let me know if that's wrong.

Thanks,
Erik

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