RE: [PATCH v2] eal: fix thread race in control thread creation

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> > >
> > > When ctrl_thread_init transitions params->ctrl_thread_status from
> > > CTRL_THREAD_LAUNCHING the creating thread and new thread may run
> > > concurrently leading to unsynchronized access to params.
> > IMO, the code will be simpler if we did not free 'params' in
> 'rte_thread_create_control'/'rte_ctrl_thread_create'. We could avoid creating
> the local copies of start_routine and the arg.
> 
> You mean in the success case i assume? it still has to be free'd if
> rte_thread_create fails.
Yes

> 
> > See more comments below.
> >
> > >
> > > This permits races for both the failure and success paths after
> > > ctrl_thread_status is stored.
> > >   * params->ret may be loaded in ctrl_thread_init failure path
> > >   * params->arg may be loaded in ctrl_thread_start or
> > >     control_thread_start when calling start_routine.
> > >
> > > For ctrl_thread_init remove the params->ret load and just return 1
> > > since it is only interpreted as a indicator of success / failure of
> ctrl_thread_init.
> > >
> > > For {ctrl,control}_thread_start store param->arg in stack allocated
> > > storage prior to calling ctrl_thread_init and use the copy when calling
> start_routine.
> > >
> > > For control_thread_start if ctrl_thread_init fails just return 0
> > > instead of loading
> > > params->ret, since the value returned is unused when
> > > params->ctrl_thread_status is set
> > > to CTRL_THREAD_ERROR when ctrl_thread_init fails.
> > >
> > > Fixes: 878b7468eacb ("eal: add platform agnostic control thread
> > > API")
> > >
> > > Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > > Reviewed-by: David Marchand <david.marchand@redhat.com>
> > > ---
> > >  lib/eal/common/eal_common_thread.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/lib/eal/common/eal_common_thread.c
> > > b/lib/eal/common/eal_common_thread.c
> > > index edb9d4e..079a385 100644
> > > --- a/lib/eal/common/eal_common_thread.c
> > > +++ b/lib/eal/common/eal_common_thread.c
> > > @@ -256,7 +256,7 @@ static int ctrl_thread_init(void *arg)
> > >  	if (params->ret != 0) {
> > >  		__atomic_store_n(&params->ctrl_thread_status,
> > >  			CTRL_THREAD_ERROR, __ATOMIC_RELEASE);
> > > -		return params->ret;
> > > +		return 1;
> > >  	}
> > >
> > >  	__atomic_store_n(&params->ctrl_thread_status,
> > > @@ -268,23 +268,25 @@ static int ctrl_thread_init(void *arg)  static
> > > void *ctrl_thread_start(void *arg)  {
> > >  	struct rte_thread_ctrl_params *params = arg;
> > > +	void *start_arg = params->arg;
> > >  	void *(*start_routine)(void *) = params->u.ctrl_start_routine;
> > These copies can be avoided, code will be much simpler
> >
> > >
> > >  	if (ctrl_thread_init(arg) != 0)
> > >  		return NULL;
> > >
> > > -	return start_routine(params->arg);
> > > +	return start_routine(start_arg);
> > We can free 'params' here after 'start_routine' returns.
> 
> I guess it doesn't matter if the allocation is retained for the duration of
> start_routine() which could be ~long.
Yes, that's what I thought, it is a small size.

> 
> David/Honnappah let me know what you decide. if you'd prefer to change to
> honnappah's suggestion i'll put a new version up.
> 
> >
> > >  }
> > >
> > >  static uint32_t control_thread_start(void *arg)  {
> > >  	struct rte_thread_ctrl_params *params = arg;
> > > +	void *start_arg = params->arg;
> > >  	rte_thread_func start_routine = params->u.control_start_routine;
> > >
> > >  	if (ctrl_thread_init(arg) != 0)
> > > -		return params->ret;
> > > +		return 0;
> > >
> > > -	return start_routine(params->arg);
> > > +	return start_routine(start_arg);
> > >  }
> > >
> > >  int
> > > --
> > > 1.8.3.1