[PATCH v4] i386: Use pthread_barrier for synchronization on tst-bz21269
Adhemerval Zanella
adhemerval.zanella@linaro.org
Tue Feb 28 14:30:11 GMT 2023
To improve the false negative in patchwork buildbot.
Checked on i686-linux-gnu and I also checked by reverting the original
bz21269 fix to pass a bogus sa_restore value (and thus triggering the
test failure).
---
sysdeps/unix/sysv/linux/i386/tst-bz21269.c | 62 +++++++---------------
1 file changed, 19 insertions(+), 43 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/i386/tst-bz21269.c b/sysdeps/unix/sysv/linux/i386/tst-bz21269.c
index 1850240c34..deaf9e5ef8 100644
--- a/sysdeps/unix/sysv/linux/i386/tst-bz21269.c
+++ b/sysdeps/unix/sysv/linux/i386/tst-bz21269.c
@@ -20,16 +20,13 @@
more specifically in do_multicpu_tests function. The main changes
are:
- - C11 atomics instead of plain access.
+ - Use pthread_barrier instead of atomic and futexes.
- Remove x86_64 support which simplifies the syscall handling
and fallbacks.
- Replicate only the test required to trigger the issue for the
BZ#21269. */
-#include <stdatomic.h>
-
#include <asm/ldt.h>
-#include <linux/futex.h>
#include <setjmp.h>
#include <signal.h>
@@ -41,6 +38,8 @@
#include <support/check.h>
#include <support/xthread.h>
+#define NITER 5
+
static int
xset_thread_area (struct user_desc *u_info)
{
@@ -55,13 +54,6 @@ xmodify_ldt (int func, const void *ptr, unsigned long bytecount)
TEST_VERIFY_EXIT (syscall (SYS_modify_ldt, 1, ptr, bytecount) == 0);
}
-static int
-futex (int *uaddr, int futex_op, int val, void *timeout, int *uaddr2,
- int val3)
-{
- return syscall (SYS_futex, uaddr, futex_op, val, timeout, uaddr2, val3);
-}
-
static void
xsethandler (int sig, void (*handler)(int, siginfo_t *, void *), int flags)
{
@@ -123,33 +115,24 @@ setup_low_user_desc (void)
low_user_desc_clear->seg_not_present = 1;
}
-/* Possible values of futex:
- 0: thread is idle.
- 1: thread armed.
- 2: thread should clear LDT entry 0.
- 3: thread should exit. */
-static atomic_uint ftx;
+static pthread_barrier_t barrier;
static void *
threadproc (void *ctx)
{
- while (1)
+ for (int i = 0; i < NITER; i++)
{
- futex ((int *) &ftx, FUTEX_WAIT, 1, NULL, NULL, 0);
- while (atomic_load (&ftx) != 2)
- {
- if (atomic_load (&ftx) >= 3)
- return NULL;
- }
+ xpthread_barrier_wait (&barrier);
/* clear LDT entry 0. */
const struct user_desc desc = { 0 };
xmodify_ldt (1, &desc, sizeof (desc));
- /* If ftx == 2, set it to zero, If ftx == 100, quit. */
- if (atomic_fetch_add (&ftx, -2) != 2)
- return NULL;
+ /* Wait for 'ss' set in main thread. */
+ xpthread_barrier_wait (&barrier);
}
+
+ return NULL;
}
@@ -180,20 +163,21 @@ do_test (void)
/* Some kernels send SIGBUS instead. */
xsethandler (SIGBUS, sigsegv_handler, 0);
+ xpthread_barrier_init (&barrier, NULL, 2);
+
thread = xpthread_create (0, threadproc, 0);
asm volatile ("mov %%ss, %0" : "=rm" (orig_ss));
- for (int i = 0; i < 5; i++)
+ for (int i = 0; i < NITER; i++)
{
if (sigsetjmp (jmpbuf, 1) != 0)
continue;
/* Make sure the thread is ready after the last test. */
- while (atomic_load (&ftx) != 0)
- ;
+ xpthread_barrier_wait (&barrier);
- struct user_desc desc = {
+ const struct user_desc desc = {
.entry_number = 0,
.base_addr = 0,
.limit = 0xffff,
@@ -207,28 +191,20 @@ do_test (void)
xmodify_ldt (0x11, &desc, sizeof (desc));
- /* Arm the thread. */
- ftx = 1;
- futex ((int*) &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
+ /* Wait thread clear LDT entry 0. */
+ xpthread_barrier_wait (&barrier);
asm volatile ("mov %0, %%ss" : : "r" (0x7));
- /* Fire up thread modify_ldt call. */
- atomic_store (&ftx, 2);
-
- while (atomic_load (&ftx) != 0)
- ;
-
/* On success, modify_ldt will segfault us synchronously and we will
escape via siglongjmp. */
support_record_failure ();
}
- atomic_store (&ftx, 100);
- futex ((int*) &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
-
xpthread_join (thread);
+ xpthread_barrier_destroy (&barrier);
+
return 0;
}
--
2.34.1
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