On Wed, Jul 24, 2019 at 3:38 AM Christian Brauner <christian@xxxxxxxxxx> wrote:
>
> On Tue, Jul 23, 2019 at 10:39:07AM -0700, Suren Baghdasaryan wrote:
> > 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")
>
> Thanks for upstreaming the stress-tester. A few comments below.
>
Thanks for the comments. All make sense. I'll send an update later
today or tomorrow.
> >
> > 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 | 137 ++++++++++++++++++
> > 3 files changed, 139 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..f2934aa070ae
> > --- /dev/null
> > +++ b/tools/testing/selftests/pidfd/pidfd_poll_test.c
> > @@ -0,0 +1,137 @@
> > +// 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"
> > +
> > +#define __NR_pidfd_send_signal 424
> > +#define __NR_pidfd_open 434
>
> That won't work on Alpha where this number is unfortunately different so
> I'm not sure which syscall you'd hit there (/me checks
> 424 common tgkill sys_tgkill
> )
>
> The better option is to just place
>
> #ifndef __NR_pidfd_send_signal
> #define __NR_pidfd_send_signal -1
> #endif
>
> #ifndef __NR_pidfd_open
> #define __NR_pidfd_open -1
> #endif
>
> into the pidfd.h header.
>
> > +
> > +static inline int sys_pidfd_open(pid_t pid, unsigned int flags)
> > +{
> > + return syscall(__NR_pidfd_open, pid, flags);
> > +}
> > +
> > +static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
> > + unsigned int flags)
> > +{
> > + return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
> > +}
>
> Those can go into pidfd.h too.
>
> > +
> > +static bool timeout;
> > +
> > +static void handle_alarm(int sig)
> > +{
> > + timeout = true;
> > +}
> > +
> > +int main(int argc, char **argv)
> > +{
> > + int ret = 1;
> > + int pidfd = -1;
> > + struct pollfd fds;
> > + int iter, nevents;
> > + int nr_iterations = 10000;
> > +
> > + fds.events = POLLIN;
>
> if (argc > 2)
> ksft_exit_fail_msg("Unexpected command line argument");
>
> > + if (argc > 1) {
>
> if (argc == 2)
>
> > + nr_iterations = atoi(argv[1]);
> > + if (!nr_iterations) {
>
> You should probably also check for negative values.
>
> > + ksft_test_result_fail("invalid input parameter %s\n",
> > + argv[1]);
> > + return ksft_exit_fail();
> > + }
> > + }
> > +
> > + ksft_print_msg("running pidfd poll test for %d iterations\n",
> > + nr_iterations);
> > +
> > + for (iter = 0; iter < nr_iterations; iter++) {
> > + int child_pid = fork();
> > +
> > + if (!child_pid) {
> > + /* Child process just sleeps for a min */
> > + sleep(60);
> > + exit(0);
>
> Just for kicks, please use exit(EXIT_SUCCESS)
>
> > + }
>
>
> You should switch the checkes, i.e.
>
> if (child_pid < 0)
> /* do stuff */
>
> if (child_pid == 0)
> /* do other stuff */
>
> > +
> > + /* Parent kills the child and waits for its death */
> > + if (child_pid < 0) {
> > + if (errno == EAGAIN) {
> > + iter--;
> > + continue;
> > + }
> > + ksft_print_msg("%s - failed to fork a child process\n",
> > + strerror(errno));
>
> Uhm, shouldn't you exit with an error here?, i.e.
>
> ksft_exit_fail_msg(...
>
> > + }
> > + pidfd = sys_pidfd_open(child_pid, 0);
> > + if (pidfd < 0) {
> > + ksft_print_msg("%s - pidfd_open failed\n",
> > + strerror(errno));
> > + goto on_error;
>
> I think you honestly can just call ksft_exit_fail_msg() everywhere. The
> fds will be cleaned up on process exit anyway and it's pretty
> short-lived.
>
> > + }
> > + /* Setup 3 sec alarm - plenty of time */
> > + if (signal(SIGALRM, handle_alarm) == SIG_ERR) {
> > + ksft_print_msg("%s - signal failed\n",
> > + strerror(errno));
> > + goto on_error;
> > + }
> > + alarm(3);
> > + /* Send SIGKILL to the child */
> > + if (sys_pidfd_send_signal(pidfd, SIGKILL, NULL, 0)) {
> > + ksft_print_msg("%s - pidfd_send_signal failed\n",
> > + strerror(errno));
> > + goto on_error;
> > + }
> > + /* Wait for the death notification */
> > + fds.fd = pidfd;
> > + nevents = poll(&fds, 1, -1);
> > + if (nevents < 0) {
> > + ksft_print_msg("%s - poll failed\n",
> > + strerror(errno));
> > + goto on_error;
> > + }
> > + if (nevents != 1) {
> > + ksft_print_msg("unexpected poll result: %d\n",
> > + nevents);
> > + goto on_error;
> > + }
> > + if (!(fds.revents & POLLIN)) {
> > + ksft_print_msg(
> > + "unexpected event type received: 0x%x\n",
> > + fds.revents);
> > + goto on_error;
> > + }
> > + if (timeout) {
> > + ksft_print_msg("death notification wait timeout\n");
> > + goto on_error;
> > + }
> > + close(pidfd);
> > + }
> > + ret = 0;
> > +
> > +on_error:
> > + if (pidfd)
> > + close(pidfd);
> > +
> > + if (ret) {
> > + ksft_test_result_fail("failed after %d retries\n", iter);
> > + return ksft_exit_fail();
> > + }
> > +
> > + ksft_test_result_pass("pidfd poll test: pass\n");
> > + return ksft_exit_pass();
> > +}
> > --
> > 2.22.0.657.g960e92d24f-goog
> >
