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    SubjectRe: [PATCH v2 4/9] selftests/harness: Fix interleaved scheduling leading to race conditions
    On Mon, Apr 29, 2024 at 03:09:26PM +0200, Mickaël Salaün wrote:
    > Fix a race condition when running several FIXTURE_TEARDOWN() managing
    > the same resource. This fixes a race condition in the Landlock file
    > system tests when creating or unmounting the same directory.
    >
    > Using clone3() with CLONE_VFORK guarantees that the child and grandchild
    > test processes are sequentially scheduled. This is implemented with a
    > new clone3_vfork() helper replacing the fork() call.
    >
    > This avoids triggering this error in __wait_for_test():
    > Test ended in some other way [127]
    >
    > Cc: Christian Brauner <brauner@kernel.org>
    > Cc: David S. Miller <davem@davemloft.net>
    > Cc: Günther Noack <gnoack@google.com>
    > Cc: Jakub Kicinski <kuba@kernel.org>
    > Cc: Kees Cook <keescook@chromium.org>
    > Cc: Mark Brown <broonie@kernel.org>
    > Cc: Shuah Khan <shuah@kernel.org>
    > Cc: Will Drewry <wad@chromium.org>
    > Fixes: 41cca0542d7c ("selftests/harness: Fix TEST_F()'s vfork handling")
    > Signed-off-by: Mickaël Salaün <mic@digikod.net>
    > Link: https://lore.kernel.org/r/20240429130931.2394118-5-mic@digikod.net
    > ---
    > tools/testing/selftests/kselftest_harness.h | 15 ++++++++++++++-
    > 1 file changed, 14 insertions(+), 1 deletion(-)
    >
    > diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
    > index 55699a762c45..9f04638707ae 100644
    > --- a/tools/testing/selftests/kselftest_harness.h
    > +++ b/tools/testing/selftests/kselftest_harness.h
    > @@ -66,6 +66,8 @@
    > #include <sys/wait.h>
    > #include <unistd.h>
    > #include <setjmp.h>
    > +#include <syscall.h>
    > +#include <linux/sched.h>
    >
    > #include "kselftest.h"
    >
    > @@ -80,6 +82,17 @@
    > # define TH_LOG_ENABLED 1
    > #endif
    >
    > +/* Wait for the child process to end but without sharing memory mapping. */
    > +static pid_t __attribute__((__unused__)) clone3_vfork(void)

    Why "unused"?

    > +{
    > + struct clone_args args = {
    > + .flags = CLONE_VFORK,
    > + .exit_signal = SIGCHLD,
    > + };
    > +
    > + return syscall(__NR_clone3, &args, sizeof(args));
    > +}
    > +
    > /**
    > * TH_LOG()
    > *
    > @@ -1183,7 +1196,7 @@ void __run_test(struct __fixture_metadata *f,
    > fflush(stdout);
    > fflush(stderr);
    >
    > - t->pid = fork();
    > + t->pid = clone3_vfork();
    > if (t->pid < 0) {
    > ksft_print_msg("ERROR SPAWNING TEST CHILD\n");
    > t->exit_code = KSFT_FAIL;

    Regardless, yup, looks good.

    Reviewed-by: Kees Cook <keescook@chromium.org>

    --
    Kees Cook

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