Re: [bug report] rcutorture: Add races with task-exit processing

[Dan Carpenter <dan.carpenter@oracle.com>]

On Wed, Apr 29, 2020 at 08:44:21AM -0700, Paul E. McKenney wrote:
> On Wed, Apr 29, 2020 at 04:24:02PM +0300, Dan Carpenter wrote:
> > Hello Paul E. McKenney,
> > 
> > The patch e02882cd57e3: "rcutorture: Add races with task-exit
> > processing" from Apr 24, 2020, leads to the following static checker
> > warning:
> > 
> > 	kernel/rcu/rcutorture.c:2429 rcu_torture_read_exit()
> > 	warn: 'rep' was already freed.
> 
> Ah, good catch, will fix!
> 
> > kernel/rcu/rcutorture.c
> >   2369  static int rcu_torture_read_exit(void *unused)
> >   2370  {
> >   2371          int count = 0;
> >   2372          bool errexit = false;
> >   2373          int i;
> >   2374          struct task_struct **rep;
> >   2375          struct torture_random_state *trsp;
> >   2376  
> >   2377          // Allocate and initialize.
> >   2378          set_user_nice(current, MAX_NICE);
> >   2379          rep = kcalloc(read_exit, sizeof(*rep), GFP_KERNEL);
> >   2380          trsp = kcalloc(read_exit, sizeof(*trsp), GFP_KERNEL);
> >   2381          if (rep && trsp) {
> >   2382                  for (i = 0; i < read_exit; i++)
> >   2383                          torture_random_init(&trsp[i]);
> >   2384                  VERBOSE_TOROUT_STRING("rcu_torture_read_exit: Start of test");
> >   2385          } else {
> >   2386                  kfree(rep);
> >                               ^^^
> >   2387                  kfree(trsp);
> >                               ^^^^
> > Freed.
> 
> And setting both rep and trsp to NULL here takes care of this, correct?
> As in kfree(NULL) is a no-op.  Or is your tool more strict?

Yes, yes.  Setting it to NULL works.  I thought about that, or returning
and I wasn't sure which was prefered.

regards,
dan carpenter