On Thu, Jul 25, 2019 at 4:58 AM Yann Droneaud <ydroneaud@xxxxxxxxxx> wrote:
>
> Hi,
>
> Le mercredi 24 juillet 2019 à 17:22 -0700, Suren Baghdasaryan a écrit :
> > This adds testing for polling on pidfd of a process being killed. Test runs
> > 10000 iterations by default to stress test pidfd polling functionality.
> > It accepts an optional command-line parameter to override the number or
> > iterations to run.
> > Specifically, it tests for:
> > - pidfd_open on a child process succeeds
> > - pidfd_send_signal on a child process succeeds
> > - polling on pidfd succeeds and returns exactly one event
> > - returned event is POLLIN
> > - event is received within 3 secs of the process being killed
> >
> > 10000 iterations was chosen because of the race condition being tested
> > which is not consistently reproducible but usually is revealed after less
> > than 2000 iterations.
> > Reveals race fixed by commit b191d6491be6 ("pidfd: fix a poll race when setting exit_state")
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > ---
> > tools/testing/selftests/pidfd/.gitignore | 1 +
> > tools/testing/selftests/pidfd/Makefile | 2 +-
> > .../testing/selftests/pidfd/pidfd_poll_test.c | 112 ++++++++++++++++++
> > 3 files changed, 114 insertions(+), 1 deletion(-)
> > create mode 100644 tools/testing/selftests/pidfd/pidfd_poll_test.c
> >
> > diff --git a/tools/testing/selftests/pidfd/.gitignore b/tools/testing/selftests/pidfd/.gitignore
> > index 16d84d117bc0..a67896347d34 100644
> > --- a/tools/testing/selftests/pidfd/.gitignore
> > +++ b/tools/testing/selftests/pidfd/.gitignore
> > @@ -1,2 +1,3 @@
> > pidfd_open_test
> > +pidfd_poll_test
> > pidfd_test
> > diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
> > index 720b2d884b3c..ed58b7108d18 100644
> > --- a/tools/testing/selftests/pidfd/Makefile
> > +++ b/tools/testing/selftests/pidfd/Makefile
> > @@ -1,7 +1,7 @@
> > # SPDX-License-Identifier: GPL-2.0-only
> > CFLAGS += -g -I../../../../usr/include/ -lpthread
> >
> > -TEST_GEN_PROGS := pidfd_test pidfd_open_test
> > +TEST_GEN_PROGS := pidfd_test pidfd_open_test pidfd_poll_test
> >
> > include ../lib.mk
> >
> > diff --git a/tools/testing/selftests/pidfd/pidfd_poll_test.c b/tools/testing/selftests/pidfd/pidfd_poll_test.c
> > new file mode 100644
> > index 000000000000..d45c612a0fe5
> > --- /dev/null
> > +++ b/tools/testing/selftests/pidfd/pidfd_poll_test.c
> > @@ -0,0 +1,112 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#define _GNU_SOURCE
> > +#include <errno.h>
> > +#include <linux/types.h>
> > +#include <linux/wait.h>
> > +#include <poll.h>
> > +#include <signal.h>
> > +#include <stdbool.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <syscall.h>
> > +#include <sys/wait.h>
> > +#include <unistd.h>
> > +
> > +#include "pidfd.h"
> > +#include "../kselftest.h"
> > +
> > +static bool timeout;
> > +
> > +static void handle_alarm(int sig)
> > +{
> > + timeout = true;
> > +}
> > +
> > +int main(int argc, char **argv)
> > +{
> > + struct pollfd fds;
> > + int iter, nevents;
> > + int nr_iterations = 10000;
> > +
> > + fds.events = POLLIN;
> > +
> > + if (argc > 2)
> > + ksft_exit_fail_msg("Unexpected command line argument\n");
> > +
> > + if (argc == 2) {
> > + nr_iterations = atoi(argv[1]);
> > + if (nr_iterations <= 0)
> > + ksft_exit_fail_msg("invalid input parameter %s\n",
> > + argv[1]);
> > + }
> > +
> > + ksft_print_msg("running pidfd poll test for %d iterations\n",
> > + nr_iterations);
> > +
> > + for (iter = 0; iter < nr_iterations; iter++) {
> > + int pidfd;
> > + int child_pid = fork();
> > +
> > + if (child_pid < 0) {
> > + if (errno == EAGAIN) {
> > + iter--;
> > + continue;
> > + }
> > + ksft_exit_fail_msg(
> > + "%s - failed to fork a child process\n",
> > + strerror(errno));
> > + }
> > +
> > + if (!child_pid) {
> > + /* Child process just sleeps for a min and exits */
> > + sleep(60);
> > + exit(EXIT_SUCCESS);
> > + }
> > +
> > + /* Parent kills the child and waits for its death */
> > + pidfd = sys_pidfd_open(child_pid, 0);
> > + if (pidfd < 0)
> > + ksft_exit_fail_msg("%s - pidfd_open failed\n",
> > + strerror(errno));
> > +
> > + /* Setup 3 sec alarm - plenty of time */
> > + if (signal(SIGALRM, handle_alarm) == SIG_ERR)
> > + ksft_exit_fail_msg("%s - signal failed\n",
> > + strerror(errno));
> > + alarm(3);
> > +
> > + /* Send SIGKILL to the child */
> > + if (sys_pidfd_send_signal(pidfd, SIGKILL, NULL, 0))
> > + ksft_exit_fail_msg("%s - pidfd_send_signal failed\n",
> > + strerror(errno));
> > +
> > + /* Wait for the death notification */
> > + fds.fd = pidfd;
> > + nevents = poll(&fds, 1, -1);
> > +
> > + /* Check for error conditions */
> > + if (nevents < 0)
> > + ksft_exit_fail_msg("%s - poll failed\n",
> > + strerror(errno));
> > +
> > + if (nevents != 1)
> > + ksft_exit_fail_msg("unexpected poll result: %d\n",
> > + nevents);
> > +
> > + if (!(fds.revents & POLLIN))
> > + ksft_exit_fail_msg(
> > + "unexpected event type received: 0x%x\n",
> > + fds.revents);
> > +
> > + if (timeout)
> > + ksft_exit_fail_msg(
> > + "death notification wait timeout\n");
> > +
> > + close(pidfd);
>
> There's no call to wait(), or alike function. Is it required for the
> test to left zombies ?
The test checks that death notification gets sent from kernel, which
by design should happen for any process that has non-zero
task->exit_state and that includes zombies (see
https://elixir.bootlin.com/linux/v5.3-rc1/source/kernel/fork.c#L1731
for that condition). So IIUC this code, the poll() should succeed no
matter if the task is zombie or dead. Or do I misunderstand your
question?
Thanks,
Suren.
>
> Regards.
>
> --
> Yann Droneaud
> OPTEYA
>
>
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