Reduce dependence on sleep duration for futex_requeue_pi_signal_restart
Detect if the initial signal was handled prior to the requeue call. If
not, re-issue the signal to ensure we test that case. This tolerates the
scenario where the waiter didn't block on f1 after the signal before the
requeue call is issued. Join the waiter after issueing the second signal
rather than sleep and then unlock. This avoids the issue where the
kernel doesn't start processing the cause for the waiter's wakeup until
after the pi lock has been released (and then gives the lock to the
waiter rather than returning EWOULDBLOCK as we intend it to).
Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
diff --git a/functional/futex_requeue_pi_signal_restart.c b/functional/futex_requeue_pi_signal_restart.c
index 8140c79..1032e7b 100644
--- a/functional/futex_requeue_pi_signal_restart.c
+++ b/functional/futex_requeue_pi_signal_restart.c
@@ -44,12 +44,11 @@
#include "futextest.h"
#include "logging.h"
-#define DELAY_US 1000
+#define DELAY_US 100
futex_t f1 = FUTEX_INITIALIZER;
futex_t f2 = FUTEX_INITIALIZER;
atomic_t requeued = ATOMIC_INITIALIZER;
-atomic_t waiter_running = ATOMIC_INITIALIZER;
typedef struct struct_waiter_arg {
long id;
@@ -113,7 +112,6 @@
info("Waiter running\n");
info("Calling FUTEX_LOCK_PI on f2=%x @ %p\n", f2, &f2);
- atomic_set(&waiter_running, 1);
old_val = f1;
res = futex_wait_requeue_pi(&f1, old_val, &(f2), NULL, FUTEX_PRIVATE_FLAG);
if (!requeued.val || errno != EWOULDBLOCK) {
@@ -178,55 +176,50 @@
futex_lock_pi(&f2, 0, 0, FUTEX_PRIVATE_FLAG);
info("m3:f2: %x\n", f2);
- /* wait for the waiter to start running, then give it time to block */
- while (!waiter_running.val)
- usleep(DELAY_US);
- usleep(DELAY_US);
-
- /*
- * signal the waiter before requeue, waiter should automatically
- * restart futex_wait_requeue_pi() in the kernel. Wait for the waiter
- * to block on f1 again.
- */
- info("Issuing SIGUSR1 to waiter\n");
- pthread_kill(waiter, SIGUSR1);
- usleep(DELAY_US);
-
- info("Waking waiter via FUTEX_CMP_REQUEUE_PI\n");
while (1) {
+ /*
+ * signal the waiter before requeue, waiter should automatically
+ * restart futex_wait_requeue_pi() in the kernel. Wait for the
+ * waiter to block on f1 again.
+ */
+ info("Issuing SIGUSR1 to waiter\n");
+ pthread_kill(waiter, SIGUSR1);
+ usleep(DELAY_US);
+
+ info("Requeueing waiter via FUTEX_CMP_REQUEUE_PI\n");
old_val = f1;
res = futex_cmp_requeue_pi(&f1, old_val, &(f2), 1, 0,
FUTEX_PRIVATE_FLAG);
- if (res)
+ /*
+ * If res is non-zero, we either requeued the waiter or hit an
+ * error, break out and handle it. If it is zero, then the
+ * signal may have hit before the the waiter was blocked on f1.
+ * Try again.
+ */
+ if (res > 0) {
+ atomic_set(&requeued, 1);
break;
- error("Waiter was not ready for requeue. First signal was "
- "delivered too early\n", 0);
- ret = RET_ERROR;
- usleep(DELAY_US);
- }
- if (res < 0) {
- error("FUTEX_CMP_REQUEUE_PI failed\n", errno);
- ret = RET_ERROR;
- } else {
- atomic_set(&requeued, 1);
+ } else if (res > 0) {
+ error("FUTEX_CMP_REQUEUE_PI failed\n", errno);
+ ret = RET_ERROR;
+ break;
+ }
}
info("m4:f2: %x\n", f2);
/*
- * signal the waiter after requeue, waiter should return from
- * futex_wait_requeue_pi() with EWOULDBLOCK.
+ * Signal the waiter after requeue, waiter should return from
+ * futex_wait_requeue_pi() with EWOULDBLOCK. Join the thread here so the
+ * futex_unlock_pi() can't happen before the signal wakeup is detected
+ * in the kernel.
*/
info("Issuing SIGUSR1 to waiter\n");
pthread_kill(waiter, SIGUSR1);
-
- /* give the signal time to get to the waiter */
- usleep(DELAY_US);
- info("Calling FUTEX_UNLOCK_PI on mutex=%x @ %p\n", f2, &f2);
- futex_unlock_pi(&f2, FUTEX_PRIVATE_FLAG);
-
- /* Wait for waiter to finish */
info("Waiting for waiter to return\n");
pthread_join(waiter, NULL);
+
+ info("Calling FUTEX_UNLOCK_PI on mutex=%x @ %p\n", f2, &f2);
+ futex_unlock_pi(&f2, FUTEX_PRIVATE_FLAG);
info("m5:f2: %x\n", f2);
out:
