On Mon, Jul 18, 2022 at 02:58:39AM +0000, lizhijian@xxxxxxxxxxx wrote: > 0Day/LKP observed that the kselftest blocks forever since one of the > pidfd_wait doesn't terminate in 1 of 30 runs. After digging into > the source, we found that it blocks at: > ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL), 0); > > wait_states has below testing flow: > CHILD PARENT > ---------------+-------------- > 1 STOP itself > 2 WAIT for CHILD STOPPED > 3 SIGNAL CHILD to CONT > 4 CONT > 5 STOP itself > 5' WAIT for CHILD CONT > 6 WAIT for CHILD STOPPED > > The problem is that the kernel cannot ensure the order of 5 and 5', once > 5's goes first, the test will fail. > > we can reproduce it by: > $ while true; do make run_tests -C pidfd; done > > Introduce a blocking read in child process to make sure the parent can > check its WCONTINUED. > > CC: Philip Li <philip.li@xxxxxxxxx> > Reported-by: kernel test robot <lkp@xxxxxxxxx> > Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx> > --- > I have almost forgotten this patch since the former version post over 6 months > ago. This time I just do a rebase and update the comments. > V2: rewrite with pipe to avoid usleep > --- Thanks for sticking with this! Reviewed-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
