[dpdk-dev] [PATCH v2] Change alarm cancel function to thread-safe:

[Michal Jastrzebski <michalx.k.jastrzebski@intel.com>]

    Change alarm cancel function to thread-safe.
    It eliminates a race between threads using rte_alarm_cancel and
    rte_alarm_set.

Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
Reviewed-by: Michal Jastrzebski <michalx.k.jastrzebski@intel.com>

---
 lib/librte_eal/common/include/rte_alarm.h |    3 +-
 lib/librte_eal/linuxapp/eal/eal_alarm.c   |   68 ++++++++++++++++++-----------
 2 files changed, 45 insertions(+), 26 deletions(-)

diff --git a/lib/librte_eal/common/include/rte_alarm.h b/lib/librte_eal/common/include/rte_alarm.h
index d451522..e7cbaef 100644
--- a/lib/librte_eal/common/include/rte_alarm.h
+++ b/lib/librte_eal/common/include/rte_alarm.h
@@ -76,7 +76,8 @@ typedef void (*rte_eal_alarm_callback)(void *arg);
 int rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb, void *cb_arg);
 
 /**
- * Function to cancel an alarm callback which has been registered before.
+ * Function to cancel an alarm callback which has been registered before. If
+ * used outside alarm callback it wait for all callbacks to finish its execution.
  *
  * @param cb_fn
  *  alarm callback
diff --git a/lib/librte_eal/linuxapp/eal/eal_alarm.c b/lib/librte_eal/linuxapp/eal/eal_alarm.c
index 480f0cb..ea8dfb4 100644
--- a/lib/librte_eal/linuxapp/eal/eal_alarm.c
+++ b/lib/librte_eal/linuxapp/eal/eal_alarm.c
@@ -69,7 +69,8 @@ struct alarm_entry {
 	struct timeval time;
 	rte_eal_alarm_callback cb_fn;
 	void *cb_arg;
-	volatile int executing;
+	volatile uint8_t executing;
+	volatile pthread_t executing_id;
 };
 
 static LIST_HEAD(alarm_list, alarm_entry) alarm_list = LIST_HEAD_INITIALIZER();
@@ -108,11 +109,13 @@ eal_alarm_callback(struct rte_intr_handle *hdl __rte_unused,
 			(ap->time.tv_sec < now.tv_sec || (ap->time.tv_sec == now.tv_sec &&
 						ap->time.tv_usec <= now.tv_usec))){
 		ap->executing = 1;
+		ap->executing_id = pthread_self();
 		rte_spinlock_unlock(&alarm_list_lk);
 
 		ap->cb_fn(ap->cb_arg);
 
 		rte_spinlock_lock(&alarm_list_lk);
+
 		LIST_REMOVE(ap, next);
 		rte_free(ap);
 	}
@@ -145,7 +148,7 @@ rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb_fn, void *cb_arg)
 	if (us < 1 || us > (UINT64_MAX - US_PER_S) || cb_fn == NULL)
 		return -EINVAL;
 
-	new_alarm = rte_malloc(NULL, sizeof(*new_alarm), 0);
+	new_alarm = rte_zmalloc(NULL, sizeof(*new_alarm), 0);
 	if (new_alarm == NULL)
 		return -ENOMEM;
 
@@ -156,7 +159,6 @@ rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb_fn, void *cb_arg)
 	new_alarm->cb_arg = cb_arg;
 	new_alarm->time.tv_usec = (now.tv_usec + us) % US_PER_S;
 	new_alarm->time.tv_sec = now.tv_sec + ((now.tv_usec + us) / US_PER_S);
-	new_alarm->executing = 0;
 
 	rte_spinlock_lock(&alarm_list_lk);
 	if (!handler_registered) {
@@ -202,34 +204,50 @@ rte_eal_alarm_cancel(rte_eal_alarm_callback cb_fn, void *cb_arg)
 {
 	struct alarm_entry *ap, *ap_prev;
 	int count = 0;
+	int executing;
 
 	if (!cb_fn)
 		return -1;
 
-	rte_spinlock_lock(&alarm_list_lk);
-	/* remove any matches at the start of the list */
-	while ((ap = LIST_FIRST(&alarm_list)) != NULL &&
-			cb_fn == ap->cb_fn && ap->executing == 0 &&
-			(cb_arg == (void *)-1 || cb_arg == ap->cb_arg)) {
-		LIST_REMOVE(ap, next);
-		rte_free(ap);
-		count++;
-	}
-	ap_prev = ap;
-
-	/* now go through list, removing entries not at start */
-	LIST_FOREACH(ap, &alarm_list, next) {
-		/* this won't be true first time through */
-		if (cb_fn == ap->cb_fn &&  ap->executing == 0 &&
+	do {
+		executing = 0;
+		rte_spinlock_lock(&alarm_list_lk);
+		/* remove any matches at the start of the list */
+		while ((ap = LIST_FIRST(&alarm_list)) != NULL &&
+				cb_fn == ap->cb_fn &&
 				(cb_arg == (void *)-1 || cb_arg == ap->cb_arg)) {
-			LIST_REMOVE(ap,next);
-			rte_free(ap);
-			count++;
-			ap = ap_prev;
+
+			if (ap->executing == 0) {
+				LIST_REMOVE(ap, next);
+				rte_free(ap);
+				count++;
+			} else {
+				if (pthread_equal(ap->executing_id, pthread_self()) == 0)
+					executing++;
+
+				break;
+			}
 		}
 		ap_prev = ap;
-	}
-	rte_spinlock_unlock(&alarm_list_lk);
+
+		/* now go through list, removing entries not at start */
+		LIST_FOREACH(ap, &alarm_list, next) {
+			/* this won't be true first time through */
+			if (cb_fn == ap->cb_fn &&
+					(cb_arg == (void *)-1 || cb_arg == ap->cb_arg)) {
+
+				if (ap->executing == 0) {
+					LIST_REMOVE(ap,next);
+					rte_free(ap);
+					count++;
+					ap = ap_prev;
+				} else if (pthread_equal(ap->executing_id, pthread_self()) == 0)
+					executing++;
+			}
+			ap_prev = ap;
+		}
+		rte_spinlock_unlock(&alarm_list_lk);
+	} while (executing != 0);
+
 	return count;
 }
-
-- 
1.7.9.5