From: "lizhijian@fujitsu.com" <lizhijian@fujitsu.com>
To: Christian Brauner <brauner@kernel.org>, Shuah Khan <shuah@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-kselftest@vger.kernel.org"
<linux-kselftest@vger.kernel.org>,
"lizhijian@fujitsu.com" <lizhijian@fujitsu.com>,
Philip Li <philip.li@intel.com>,
kernel test robot <lkp@intel.com>
Subject: [PATCH] ksefltest: pidfd: Fix wait_states: Test terminated by timeout
Date: Mon, 18 Jul 2022 02:58:39 +0000 [thread overview]
Message-ID: <20220718025826.29148-1-lizhijian@fujitsu.com> (raw)
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
---
tools/testing/selftests/pidfd/pidfd_wait.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c
index 070c1c876df1..3f7bc6517dea 100644
--- a/tools/testing/selftests/pidfd/pidfd_wait.c
+++ b/tools/testing/selftests/pidfd/pidfd_wait.c
@@ -95,20 +95,27 @@ TEST(wait_states)
.flags = CLONE_PIDFD | CLONE_PARENT_SETTID,
.exit_signal = SIGCHLD,
};
+ int ret, pfd[2];
pid_t pid;
siginfo_t info = {
.si_signo = 0,
};
+ ASSERT_EQ(pipe(pfd), 0);
pid = sys_clone3(&args);
ASSERT_GE(pid, 0);
if (pid == 0) {
+ char buf[2];
+ close(pfd[1]);
kill(getpid(), SIGSTOP);
+ ASSERT_EQ(read(pfd[0], buf, 1), 1);
+ close(pfd[0]);
kill(getpid(), SIGSTOP);
exit(EXIT_SUCCESS);
}
+ close(pfd[0]);
ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WSTOPPED, NULL), 0);
ASSERT_EQ(info.si_signo, SIGCHLD);
ASSERT_EQ(info.si_code, CLD_STOPPED);
@@ -117,6 +124,8 @@ TEST(wait_states)
ASSERT_EQ(sys_pidfd_send_signal(pidfd, SIGCONT, NULL, 0), 0);
ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL), 0);
+ ASSERT_EQ(write(pfd[1], "C", 1), 1);
+ close(pfd[1]);
ASSERT_EQ(info.si_signo, SIGCHLD);
ASSERT_EQ(info.si_code, CLD_CONTINUED);
ASSERT_EQ(info.si_pid, parent_tid);
--
2.36.0
next reply other threads:[~2022-07-18 2:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-18 2:58 lizhijian [this message]
2022-07-18 3:08 ` [PATCH] ksefltest: pidfd: Fix wait_states: Test terminated by timeout lizhijian
2022-07-19 8:32 ` Christian Brauner
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