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SubjectRe: [PATCH] ksefltest: pidfd: Fix wait_states: Test terminated by timeout
On Mon, Jul 18, 2022 at 02:58:39AM +0000, lizhijian@fujitsu.com 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@intel.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
> ---
> 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@kernel.org>

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