Re: [PATCH v2] service: fix race in service on app lcore function

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Nov 01, 2017 at 06:48:01PM +0000, Harry van Haaren wrote:
> This commit fixes a possible race condition if an application
> uses the service-cores infrastructure and the function to run
> a service on an application lcore at the same time.
> 
> The fix is to change the num_mapped_cores variable to be an
> atomic variable. This causes concurrent accesses by multiple
> threads to a service using rte_service_run_iter_on_app_lcore()
> to detect if another core is currently mapped to the service,
> and refuses to run if it is not multi-thread safe.
> 
> The run iteration on app lcore function has two arguments, the
> service id to run, and if atomics should be used to serialize access
> to multi-thread unsafe services. This allows applications to choose
> if they wish to use use the service-cores feature, or if they
> take responsibility themselves for serializing invoking a service.
> See doxygen documentation for more details.
> 
> Two unit tests were added to verify the behaviour of the
> function to run a service on an application core, testing both
> a multi-thread safe service, and a multi-thread unsafe service.
> 
> The doxygen API documentation for the function has been updated
> to reflect the current and correct behaviour.
> 
> Fixes: e9139a32f6e8 ("service: add function to run on app lcore")
> 
> Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
> 
> ---
> 
> v2:
> - Rework function to have parameter that allows the application
>   to select if it requires atomics to be used of it the application
>   wishes to take responsibility for serializing instead.
> 
This approach seems better to me. I think the function itself might be
better if you just duplicated a bit more code to reduce the number of
checks on the serialization variable, but it's readable enough as it is
now, so

Acked-by: Bruce Richardson <bruce.richardson@intel.com>