| Message ID | 20240511171445.904356-5-mic@digikod.net |
|---|---|
| State | Accepted |
| Commit | a86f18903db9211e265cc130b61adb175b7a4c42 |
| Headers | show |
| Series | Fix Kselftest's vfork() side effects | expand |
On Sat, May 11, 2024 at 07:14:39PM +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 is now in mainline and appears to be causing several tests (at least the ptrace vmaccess global_attach test on arm64, possibly also some of the epoll tests) that previously were timed out by the harness to to hang instead. A bisect seems to point at this patch in particular, there was a bunch of discussion of the fallout of these patches but I'm afraid I lost track of it, is there something in flight for this? -next is affected as well from the looks of it. Log of the ptrace issue (not that it's useful, the job just gets killed by the test runner): https://lava.sirena.org.uk/scheduler/job/307984 Bisect log: git bisect start # status: waiting for both good and bad commits # good: [e8f897f4afef0031fe618a8e94127a0934896aba] Linux 6.8 git bisect good e8f897f4afef0031fe618a8e94127a0934896aba # status: waiting for bad commit, 1 good commit known # bad: [a38297e3fb012ddfa7ce0321a7e5a8daeb1872b6] Linux 6.9 git bisect bad a38297e3fb012ddfa7ce0321a7e5a8daeb1872b6 # good: [480e035fc4c714fb5536e64ab9db04fedc89e910] Merge tag 'drm-next-2024-03-13' of https://gitlab.freedesktop.org/drm/kernel git bisect good 480e035fc4c714fb5536e64ab9db04fedc89e910 # good: [2ac2b1665d3fbec6ca709dd6ef3ea05f4a51ee4c] Merge tag 'hwlock-v6.9' of git://git.kernel.org/pub/scm/linux/kernel/git/remoteproc/linux git bisect good 2ac2b1665d3fbec6ca709dd6ef3ea05f4a51ee4c # good: [e858beeddfa3a400844c0e22d2118b3b52f1ea5e] bcachefs: If we run merges at a lower watermark, they must be nonblocking git bisect good e858beeddfa3a400844c0e22d2118b3b52f1ea5e # good: [e43afae4a335ac0bf54c7a8f23ed65dd55449649] Merge tag 'powerpc-6.9-3' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux git bisect good e43afae4a335ac0bf54c7a8f23ed65dd55449649 # good: [09e10499ee6a5a89fc352f25881276398a49596a] Merge tag 'drm-misc-fixes-2024-05-02' of https://gitlab.freedesktop.org/drm/misc/kernel into drm-fixes git bisect good 09e10499ee6a5a89fc352f25881276398a49596a # good: [3c15237018eb8a9a56bb49a5dbf4d8eeb154b5cc] Merge tag 'usb-6.9-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb git bisect good 3c15237018eb8a9a56bb49a5dbf4d8eeb154b5cc # good: [62788b0f225da1837ad38101112e2c49123470ee] Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rmk/linux git bisect good 62788b0f225da1837ad38101112e2c49123470ee # good: [ed44935c330a2633440e8d2660db3c7538eeaf10] Merge tag 'spi-fix-v6.9-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi git bisect good ed44935c330a2633440e8d2660db3c7538eeaf10 # good: [c22c3e0753807feee1391a22228b0d5e6ba39b74] Merge tag 'mm-hotfixes-stable-2024-05-10-13-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm git bisect good c22c3e0753807feee1391a22228b0d5e6ba39b74 # good: [b61821bb32c5577272408e1b05e6a0879a64257f] Merge tag 'drm-misc-fixes-2024-05-10' of https://gitlab.freedesktop.org/drm/misc/kernel into drm-fixes git bisect good b61821bb32c5577272408e1b05e6a0879a64257f # bad: [323feb3bdb67649bfa5614eb24ec9cb92a60cf33] selftests/harness: Handle TEST_F()'s explicit exit codes git bisect bad 323feb3bdb67649bfa5614eb24ec9cb92a60cf33 # bad: [323feb3bdb67649bfa5614eb24ec9cb92a60cf33] selftests/harness: Handle TEST_F()'s explicit exit codes git bisect bad 323feb3bdb67649bfa5614eb24ec9cb92a60cf33 # bad: [3656bc23429a4d539c81b5cb8f17ceeeeca8901a] selftests/landlock: Do not allocate memory in fixture data git bisect bad 3656bc23429a4d539c81b5cb8f17ceeeeca8901a # good: [7e4042abe2ee7c0977fd8bb049a6991b174a5e6f] selftests/landlock: Fix FS tests when run on a private mount point git bisect good 7e4042abe2ee7c0977fd8bb049a6991b174a5e6f # bad: [a86f18903db9211e265cc130b61adb175b7a4c42] selftests/harness: Fix interleaved scheduling leading to race conditions git bisect bad a86f18903db9211e265cc130b61adb175b7a4c42 # good: [fff37bd32c7605d93bf900c4c318d56d12000048] selftests/harness: Fix fixture teardown git bisect good fff37bd32c7605d93bf900c4c318d56d12000048 # first bad commit: [a86f18903db9211e265cc130b61adb175b7a4c42] selftests/harness: Fix interleaved scheduling leading to race conditions
diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h index 55699a762c45..9d7178a71c2c 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 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() * @@ -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;
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: 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") Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Mickaël Salaün <mic@digikod.net> Link: https://lore.kernel.org/r/20240511171445.904356-5-mic@digikod.net --- Changes since v2: * Replace __attribute__((__unused__)) with inline for clone3_vfork() (suggested by Kees and Jakub) --- tools/testing/selftests/kselftest_harness.h | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)