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Date: Tue, 25 Jun 2024 09:30:07 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: Mark Brown <broonie@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
Kees Cook <keescook@...omium.org>, Shuah Khan <shuah@...nel.org>,
Shuah Khan <skhan@...uxfoundation.org>
Cc: Christian Brauner <brauner@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>, Sean Christopherson <seanjc@...gle.com>,
Bagas Sanjaya <bagasdotme@...il.com>, Shengyu Li <shengyu.li.evgeny@...il.com>,
Brendan Higgins <brendanhiggins@...gle.com>, David Gow <davidgow@...gle.com>,
"David S . Miller" <davem@...emloft.net>, Florian Fainelli <florian.fainelli@...adcom.com>,
Günther Noack <gnoack@...gle.com>, Jon Hunter <jonathanh@...dia.com>, Ron Economos <re@...z.net>,
Ronald Warsow <rwarsow@....de>, Stephen Rothwell <sfr@...b.auug.org.au>,
Will Drewry <wad@...omium.org>, kernel test robot <oliver.sang@...el.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, netdev@...r.kernel.org,
stable@...r.kernel.org
Subject: Re: [PATCH v1] selftests/harness: Fix tests timeout and race
condition
I pushed it to my next branch.
Mark, Shuah, and others, please let me know if kselftest and KernelCI
are better with that.
On Fri, Jun 21, 2024 at 08:06:05PM +0200, Mickaël Salaün wrote:
> We cannot use CLONE_VFORK because we also need to wait for the timeout
> signal.
>
> Restore tests timeout by using the original fork() call in __run_test()
> but also in __TEST_F_IMPL(). Also fix a race condition when waiting for
> the test child process.
>
> Because test metadata are shared between test processes, only the
> parent process must set the test PID (child). Otherwise, t->pid may be
> set to zero, leading to inconsistent error cases:
>
> # RUN layout1.rule_on_mountpoint ...
> # rule_on_mountpoint: Test ended in some other way [127]
> # OK layout1.rule_on_mountpoint
> ok 20 layout1.rule_on_mountpoint
>
> As safeguards, initialize the "status" variable with a valid exit code,
> and handle unknown test exits as errors.
>
> The use of fork() introduces a new race condition in landlock/fs_test.c
> which seems to be specific to hostfs bind mounts, but I haven't found
> the root cause and it's difficult to trigger. I'll try to fix it with
> another patch.
>
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: Günther Noack <gnoack@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Will Drewry <wad@...omium.org>
> Cc: stable@...r.kernel.org
> Closes: https://lore.kernel.org/r/9341d4db-5e21-418c-bf9e-9ae2da7877e1@sirena.org.uk
> Fixes: a86f18903db9 ("selftests/harness: Fix interleaved scheduling leading to race conditions")
> Fixes: 24cf65a62266 ("selftests/harness: Share _metadata between forked processes")
> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> Link: https://lore.kernel.org/r/20240621180605.834676-1-mic@digikod.net
> ---
> tools/testing/selftests/kselftest_harness.h | 43 ++++++++++++---------
> 1 file changed, 24 insertions(+), 19 deletions(-)
>
> diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
> index b634969cbb6f..40723a6a083f 100644
> --- a/tools/testing/selftests/kselftest_harness.h
> +++ b/tools/testing/selftests/kselftest_harness.h
> @@ -66,8 +66,6 @@
> #include <sys/wait.h>
> #include <unistd.h>
> #include <setjmp.h>
> -#include <syscall.h>
> -#include <linux/sched.h>
>
> #include "kselftest.h"
>
> @@ -82,17 +80,6 @@
> # define TH_LOG_ENABLED 1
> #endif
>
> -/* Wait for the child process to end but without sharing memory mapping. */
> -static inline pid_t clone3_vfork(void)
> -{
> - struct clone_args args = {
> - .flags = CLONE_VFORK,
> - .exit_signal = SIGCHLD,
> - };
> -
> - return syscall(__NR_clone3, &args, sizeof(args));
> -}
> -
> /**
> * TH_LOG()
> *
> @@ -437,7 +424,7 @@ static inline pid_t clone3_vfork(void)
> } \
> if (setjmp(_metadata->env) == 0) { \
> /* _metadata and potentially self are shared with all forks. */ \
> - child = clone3_vfork(); \
> + child = fork(); \
> if (child == 0) { \
> fixture_name##_setup(_metadata, self, variant->data); \
> /* Let setup failure terminate early. */ \
> @@ -1016,7 +1003,14 @@ void __wait_for_test(struct __test_metadata *t)
> .sa_flags = SA_SIGINFO,
> };
> struct sigaction saved_action;
> - int status;
> + /*
> + * Sets status so that WIFEXITED(status) returns true and
> + * WEXITSTATUS(status) returns KSFT_FAIL. This safe default value
> + * should never be evaluated because of the waitpid(2) check and
> + * SIGALRM handling.
> + */
> + int status = KSFT_FAIL << 8;
> + int child;
>
> if (sigaction(SIGALRM, &action, &saved_action)) {
> t->exit_code = KSFT_FAIL;
> @@ -1028,7 +1022,15 @@ void __wait_for_test(struct __test_metadata *t)
> __active_test = t;
> t->timed_out = false;
> alarm(t->timeout);
> - waitpid(t->pid, &status, 0);
> + child = waitpid(t->pid, &status, 0);
> + if (child == -1 && errno != EINTR) {
> + t->exit_code = KSFT_FAIL;
> + fprintf(TH_LOG_STREAM,
> + "# %s: Failed to wait for PID %d (errno: %d)\n",
> + t->name, t->pid, errno);
> + return;
> + }
> +
> alarm(0);
> if (sigaction(SIGALRM, &saved_action, NULL)) {
> t->exit_code = KSFT_FAIL;
> @@ -1083,6 +1085,7 @@ void __wait_for_test(struct __test_metadata *t)
> WTERMSIG(status));
> }
> } else {
> + t->exit_code = KSFT_FAIL;
> fprintf(TH_LOG_STREAM,
> "# %s: Test ended in some other way [%u]\n",
> t->name,
> @@ -1218,6 +1221,7 @@ void __run_test(struct __fixture_metadata *f,
> struct __test_xfail *xfail;
> char test_name[1024];
> const char *diagnostic;
> + int child;
>
> /* reset test struct */
> t->exit_code = KSFT_PASS;
> @@ -1236,15 +1240,16 @@ void __run_test(struct __fixture_metadata *f,
> fflush(stdout);
> fflush(stderr);
>
> - t->pid = clone3_vfork();
> - if (t->pid < 0) {
> + child = fork();
> + if (child < 0) {
> ksft_print_msg("ERROR SPAWNING TEST CHILD\n");
> t->exit_code = KSFT_FAIL;
> - } else if (t->pid == 0) {
> + } else if (child == 0) {
> setpgrp();
> t->fn(t, variant);
> _exit(t->exit_code);
> } else {
> + t->pid = child;
> __wait_for_test(t);
> }
> ksft_print_msg(" %4s %s\n",
>
> base-commit: 83a7eefedc9b56fe7bfeff13b6c7356688ffa670
> --
> 2.45.2
>
>
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