Re: [dpdk-dev] [PATCH v2] test: fix debug autotest with eal cleanup addition

["Van Haaren, Harry" <harry.van.haaren@intel.com>]

> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> Sent: Wednesday, January 31, 2018 2:32 PM
> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Van Haaren, Harry
> <harry.van.haaren@intel.com>
> Cc: dev@dpdk.org; pbhagavatula@caviumnetworks.com
> Subject: Re: [dpdk-dev] [PATCH v2] test: fix debug autotest with eal cleanup
> addition
> 
> 31/01/2018 14:53, Ananyev, Konstantin:
> > Hi Harry,
> >
> > From: Harry van Haaren
> > >
> > > Before this patch, the debug_autotest would call fork(),
> > > call rte_panic() or rte_exit() in the child process, and
> > > examine the return code to verify that rte_panic() and
> > > rte_exit() were correctly reporting failures.
> > >
> > > With the inclusion of the rte_eal_cleanup() patch, rte_exit()
> > > was modified to cleanly tear-down EAL allocations. Currently
> > > only one library (service cores) is allocated by EAL at startup
> > > and should be cleaned up. This library has a check on a normal
> > > (non-hugepage) variable to protect against double cleanup. The
> > > service cores finalize() function itself frees back hugepage mem.
> > >
> > > Given the fork() approach from the unit test, and the fact that
> > > the double-free check is on an ordinary variable, causes multiple
> > > child processed (fork()-ed from the unit-test runner) to attempt
> > > to free the huge-page memory multiple times. The variable to
> > > protect against double-cleanup was not effective, as the fork()
> > > would restore it to show initialized in the next child.
> > >
> > > The solution is to call rte_service_finalize() *before* calling
> > > fork(), which results in the service cores double-cleanup variable
> > > to be zero before the fork(), and hence the child processes never
> > > free the hugepage service-cores memory (correct behavior, as the
> > > unit-test suite is still running, and owns the hugepages).
> >
> > Ok, you fixed it in UT, but what to do other apps that use fork()?
> > Let say our examples/multi_process/l2fwd_fork uses fork() to
> > spawn child processes instead of threads.
> > Might be some generic way is needed: let say at fork time setup some
> > global to indicate that it is a child process and it shouldn't call
> rte_finalize() or so.
> > Konstantin

Valid concerns, the issue gets complex when we mix shared resources
and fork() multiple processes, threads etc.


> At first, we should discuss whether it is a good idea to support fork,
> given that we have the "secondary process solution".
> 
> Then, if an improvement is needed, it should go in 18.05.
> I think the fix in UT is good enough for 18.02.

Agreed, and I'd prefer not rush changes here given
the complexity and multitude of use-cases.