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

[Thomas Monjalon <thomas@monjalon.net>]

02/11/2017 10:41, Bruce Richardson:
> 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>

Applied, thanks