On 8/31/22 21:10, Li Zhijian 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 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> Reviewed-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx> ---
Sorry for the delay. Now applied to linux-kselftest fixes for rc4 thanks, -- Shuah
