Patch "ksefltests: pidfd: Fix wait_states: Test terminated by timeout" has been added to the 6.0-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ksefltests: pidfd: Fix wait_states: Test terminated by timeout

to the 6.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ksefltests-pidfd-fix-wait_states-test-terminated-by-.patch
and it can be found in the queue-6.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 17c27be9a7fb7e927b7f93ec9ed9c87c8e231afc
Author: Li Zhijian <lizhijian@xxxxxxxxxxx>
Date:   Thu Sep 1 03:10:07 2022 +0000

    ksefltests: pidfd: Fix wait_states: Test terminated by timeout
    
    [ Upstream commit 88e1f16ba58665e9edfce437ea487da2fa759af9 ]
    
    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>
    Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c
index 070c1c876df1..c3e2a3041f55 100644
--- a/tools/testing/selftests/pidfd/pidfd_wait.c
+++ b/tools/testing/selftests/pidfd/pidfd_wait.c
@@ -95,20 +95,28 @@ TEST(wait_states)
 		.flags = CLONE_PIDFD | CLONE_PARENT_SETTID,
 		.exit_signal = SIGCHLD,
 	};
+	int 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 +125,8 @@ 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);