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@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Günther Noack <gnoack@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Will Drewry <wad@xxxxxxxxxxxx>
Fixes: 41cca0542d7c ("selftests/harness: Fix TEST_F()'s vfork handling")
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240511171445.904356-5-mic@xxxxxxxxxxx
---
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(-)
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;
--
2.45.0
