[LTP] [PATCH v2] syscalls/tgkill03: wait for defunct tid to get detached

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> On Mon, Jun 17, 2019 at 3:34 PM Jan Stancek <jstancek@redhat.com> wrote:
> 
> > Case where defunct tid is used has been observed to sporadically fail:
> >   tgkill03.c:96: FAIL: Defunct tid should have failed with ESRCH: SUCCESS
> >
> > glibc __pthread_timedjoin_ex() waits for CLONE_CHILD_CLEARTID to clear tid,
> > and then resumes. Kernel clears it (glibc pd->tid) at:
> >   do_exit
> >     exit_mm
> >       mm_release
> >         put_user(0, tsk->clear_child_tid);
> >
> > but kernel tid is still valid, presumably until:
> >   release_task
> >     __exit_signal
> >       __unhash_process
> >         detach_pid
> >
> > To avoid race wait until /proc/<pid>/task/<tid> disappears.
> >
> > Signed-off-by: Jan Stancek <jstancek@redhat.com>
> > ---
> >  testcases/kernel/syscalls/tgkill/tgkill03.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > Changes in v2:
> >   - use helper func suggested by Li (with higher timeout)
> >   - not tested, trying to get s390x to confirm
> >
> > diff --git a/testcases/kernel/syscalls/tgkill/tgkill03.c
> > b/testcases/kernel/syscalls/tgkill/tgkill03.c
> > index f5bbdc5a8d4e..ce046f576b5f 100644
> > --- a/testcases/kernel/syscalls/tgkill/tgkill03.c
> > +++ b/testcases/kernel/syscalls/tgkill/tgkill03.c
> > @@ -7,6 +7,7 @@
> >
> >  #include <pthread.h>
> >  #include <pwd.h>
> > +#include <stdio.h>
> >  #include <sys/types.h>
> >
> >  #include "tst_safe_pthread.h"
> > @@ -42,6 +43,7 @@ static void setup(void)
> >  {
> >         sigset_t sigusr1;
> >         pthread_t defunct_thread;
> > +       char defunct_tid_path[PATH_MAX];
> >
> >         sigemptyset(&sigusr1);
> >         sigaddset(&sigusr1, SIGUSR1);
> > @@ -55,8 +57,9 @@ static void setup(void)
> >         TST_CHECKPOINT_WAIT(0);
> >
> >         SAFE_PTHREAD_CREATE(&defunct_thread, NULL, defunct_thread_func,
> > NULL);
> > -
> >         SAFE_PTHREAD_JOIN(defunct_thread, NULL);
> > +       sprintf(defunct_tid_path, "/proc/%d/task/%d", getpid(),
> > defunct_tid);
> > +       TST_RETRY_FN_EXP_BACKOFF(access(defunct_tid_path, R_OK), -1, 15);
> >  }
> >
> >  static void cleanup(void)
> > @@ -108,4 +111,5 @@ static struct tst_test test = {
> >         .setup = setup,
> >         .cleanup = cleanup,
> >         .test = run,
> > +       .timeout = 15,
> >
> 
> I'd like to give a little bit more time here which larger than the
> exponential backoff macro time.

I bumped it to 20 and pushed.

Thanks,
Jan