On Thu, Sep 24, 2020 at 04:33:17PM +0200, Christian Brauner wrote:

On Wed, Sep 23, 2020 at 07:52:05PM +0530, Naresh Kamboju wrote:

...

selftests: pidfd: pidfd_wait hangs on linux next kernel on x86_64, i386 and arm64 Juno-r2 These devices are using NFS mounted rootfs. I have tested pidfd testcases independently and all test PASS.

The Hang or exit from test run noticed when run by run_kselftest.sh

pidfd_wait.c:208:wait_nonblock:Expected sys_waitid(P_PIDFD, pidfd, &info, WSTOPPED, NULL) (-1) == 0 (0) wait_nonblock: Test terminated by assertion

metadata: git branch: master git repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git git commit: e64997027d5f171148687e58b78c8b3c869a6158 git describe: next-20200922 make_kernelversion: 5.9.0-rc6 kernel-config: http://snapshots.linaro.org/openembedded/lkft/lkft/sumo/intel-core2-32/lkft/...

Reported-by: Naresh Kamboju naresh.kamboju@linaro.org

Thanks for reproting this. I'm taking a look now!

Ok, this is a simple race in the selftests, that I overlooked and which is more likely to hit when there's a lot of processes running on the system. Basically the child process hasn't SIGSTOPed itself yet but the parent is already calling waitid() on a O_NONBLOCK pidfd. Since it doesn't find a WSTOPPED process it returns -EAGAIN correctly.

The fix for this is to move the line where we're removing the O_NONBLOCK property from the fd before the waitid() WSTOPPED call so we hang until the child becomes stopped.

So I believe the fix is:

diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c index 4063d6f31fa4..be2943f072f6 100644 --- a/tools/testing/selftests/pidfd/pidfd_wait.c +++ b/tools/testing/selftests/pidfd/pidfd_wait.c @@ -205,6 +205,8 @@ TEST(wait_nonblock) ret = sys_waitid(P_PIDFD, pidfd, &info, WEXITED | WNOHANG, NULL); ASSERT_EQ(ret, 0);

+ ASSERT_EQ(fcntl(pidfd, F_SETFL, (flags & ~O_NONBLOCK)), 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); @@ -212,8 +214,6 @@ TEST(wait_nonblock)

ASSERT_EQ(sys_pidfd_send_signal(pidfd, SIGCONT, NULL, 0), 0);

- ASSERT_EQ(fcntl(pidfd, F_SETFL, (flags & ~O_NONBLOCK)), 0); - ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WEXITED, NULL), 0); ASSERT_EQ(info.si_signo, SIGCHLD); ASSERT_EQ(info.si_code, CLD_EXITED);

Christian

On Thu, 24 Sep 2020 at 21:51, Christian Brauner christian.brauner@ubuntu.com wrote:

On Thu, Sep 24, 2020 at 04:33:17PM +0200, Christian Brauner wrote:

...

On Wed, Sep 23, 2020 at 07:52:05PM +0530, Naresh Kamboju wrote:

...

selftests: pidfd: pidfd_wait hangs on linux next kernel on x86_64, i386 and arm64 Juno-r2 These devices are using NFS mounted rootfs. I have tested pidfd testcases independently and all test PASS.

The Hang or exit from test run noticed when run by run_kselftest.sh

pidfd_wait.c:208:wait_nonblock:Expected sys_waitid(P_PIDFD, pidfd, &info, WSTOPPED, NULL) (-1) == 0 (0) wait_nonblock: Test terminated by assertion

metadata: git branch: master git repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git git commit: e64997027d5f171148687e58b78c8b3c869a6158 git describe: next-20200922 make_kernelversion: 5.9.0-rc6 kernel-config: http://snapshots.linaro.org/openembedded/lkft/lkft/sumo/intel-core2-32/lkft/...

Reported-by: Naresh Kamboju naresh.kamboju@linaro.org

Thanks for reproting this. I'm taking a look now!

Ok, this is a simple race in the selftests, that I overlooked and which is more likely to hit when there's a lot of processes running on the system. Basically the child process hasn't SIGSTOPed itself yet but the parent is already calling waitid() on a O_NONBLOCK pidfd. Since it doesn't find a WSTOPPED process it returns -EAGAIN correctly.

The fix for this is to move the line where we're removing the O_NONBLOCK property from the fd before the waitid() WSTOPPED call so we hang until the child becomes stopped.

So I believe the fix is:

I have tested this patch and the pidfd_wait test did not hang this time.

Tested-by: Naresh Kamboju naresh.kamboju@linaro.org

test log link https://lkft.validation.linaro.org/scheduler/job/1813223

diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c index 4063d6f31fa4..be2943f072f6 100644 --- a/tools/testing/selftests/pidfd/pidfd_wait.c +++ b/tools/testing/selftests/pidfd/pidfd_wait.c @@ -205,6 +205,8 @@ TEST(wait_nonblock) ret = sys_waitid(P_PIDFD, pidfd, &info, WEXITED | WNOHANG, NULL); ASSERT_EQ(ret, 0);

•   ASSERT_EQ(fcntl(pidfd, F_SETFL, (flags & ~O_NONBLOCK)), 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);
  

@@ -212,8 +214,6 @@ TEST(wait_nonblock)

    ASSERT_EQ(sys_pidfd_send_signal(pidfd, SIGCONT, NULL, 0), 0);

•   ASSERT_EQ(fcntl(pidfd, F_SETFL, (flags & ~O_NONBLOCK)), 0);
  

•   ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WEXITED, NULL), 0);
    ASSERT_EQ(info.si_signo, SIGCHLD);
    ASSERT_EQ(info.si_code, CLD_EXITED);
  
  

- Naresh

Christian