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

[Tyler Retzlaff <roretzla@linux.microsoft.com>]

On Thu, Mar 02, 2023 at 01:30:13AM +0000, Honnappa Nagarahalli wrote:
> 
> 
> > -----Original Message-----
> > From: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > Sent: Wednesday, March 1, 2023 3:10 PM
> > To: dev@dpdk.org; david.marchand@redhat.com
> > Cc: thomas@monjalon.net; Tyler Retzlaff <roretzla@linux.microsoft.com>
> > Subject: [PATCH v2] eal: fix thread race in control thread creation
> > 
> > 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.

> 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 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.

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