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

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

On 03-May-19 11:54 PM, Erik Gabriel Carrillo wrote:
> The finalize function should free the memzone created in the init
> function, rather than freeing the allocation the memzone references,
> otherwise a memzone descriptor can be leaked.
> 
> Fixes: c0749f7096c7 ("timer: allow management in shared memory")
> 
> Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
> ---
> changes in v2:
>   - Handle scenario where primary process exits before secondaries such
>     that memzone is not freed early (Anatoly)
> 
>   lib/librte_timer/rte_timer.c | 20 +++++++++++++++++---
>   1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_timer/rte_timer.c b/lib/librte_timer/rte_timer.c
> index eb46009..4771287 100644
> --- a/lib/librte_timer/rte_timer.c
> +++ b/lib/librte_timer/rte_timer.c
> @@ -60,6 +60,8 @@ struct rte_timer_data {
>   };
>   
>   #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?

>   
>   	if (rte_timer_subsystem_initialized)
>   		return -EALREADY;
> @@ -164,10 +167,14 @@ rte_timer_subsystem_init_v1905(void)
>   		if (mz == NULL)
>   			return -EEXIST;
>   
> +		rte_timer_data_mz = mz;
>   		rte_timer_data_arr = mz->addr;
> +		rte_timer_mz_refcnt =
> +				(void *)((char *)mz->addr + data_arr_size);
>   
>   		rte_timer_data_arr[default_data_id].internal_flags |=
>   			FL_ALLOCATED;
> +		rte_atomic16_inc(rte_timer_mz_refcnt);
>   
>   		rte_timer_subsystem_initialized = 1;
>   
> @@ -175,12 +182,15 @@ rte_timer_subsystem_init_v1905(void)
>   	}
>   
>   	mz = rte_memzone_reserve_aligned(mz_name,
> -			RTE_MAX_DATA_ELS * sizeof(*rte_timer_data_arr),
> +			data_arr_size + sizeof(*rte_timer_mz_refcnt),
>   			SOCKET_ID_ANY, 0, RTE_CACHE_LINE_SIZE);
>   	if (mz == NULL)
>   		return -ENOMEM;
>   
> +	rte_timer_data_mz = mz;
>   	rte_timer_data_arr = mz->addr;
> +	rte_timer_mz_refcnt = (void *)((char *)mz->addr + data_arr_size);
> +	rte_atomic16_init(rte_timer_mz_refcnt);
>   
>   	for (i = 0; i < RTE_MAX_DATA_ELS; i++) {
>   		data = &rte_timer_data_arr[i];
> @@ -193,6 +203,7 @@ rte_timer_subsystem_init_v1905(void)
>   	}
>   
>   	rte_timer_data_arr[default_data_id].internal_flags |= FL_ALLOCATED;
> +	rte_atomic16_inc(rte_timer_mz_refcnt);
>   
>   	rte_timer_subsystem_initialized = 1;
>   
> @@ -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 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.

>   
>   	rte_timer_subsystem_initialized = 0;
>   }
> 


-- 
Thanks,
Anatoly