target: fix timer callbacks processing

Warning, behaviour change: before this patch if a timer callback
returned an error, the other handlers in the list were not called.

This patch fixes two different issues with the way timer callbacks are
called:

1. The function is not designed to be reentrant but a nested call is
possible via: target_handle timer event -> poll -> target events
before/after reexaminantion -> script_command_run ->
target_call_timer_callbacks_now . This patch makes function a no-op
when called recursively;

2. The current code can deal with the case when calling a handler
leads to its removal but not when it leads to removal of the next
callback in the list. This patch defers actual removal to consolidate
it with the calling loop.

These bugs were exposed by Valgrind.

Change-Id: Ia628a744634f5d2911eb329747e826cb9772e789
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2541
Tested-by: jenkins
Reviewed-by: Stian Skjelstad <stian@nixia.no>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/target/target.c

@@ -1378,6 +1378,7 @@ int target_register_timer_callback(int (*callback)(void *priv), int time_ms, int
 	(*callbacks_p)->callback = callback;
 	(*callbacks_p)->periodic = periodic;
 	(*callbacks_p)->time_ms = time_ms;
+	(*callbacks_p)->removed = false;
 
 	gettimeofday(&now, NULL);
 	(*callbacks_p)->when.tv_usec = now.tv_usec + (time_ms % 1000) * 1000;
@@ -1438,24 +1439,18 @@ int target_unregister_reset_callback(int (*callback)(struct target *target,
 
 int target_unregister_timer_callback(int (*callback)(void *priv), void *priv)
 {
-	struct target_timer_callback **p = &target_timer_callbacks;
-	struct target_timer_callback *c = target_timer_callbacks;
-
 	if (callback == NULL)
 		return ERROR_COMMAND_SYNTAX_ERROR;
 
-	while (c) {
-		struct target_timer_callback *next = c->next;
+	for (struct target_timer_callback *c = target_timer_callbacks;
+	     c; c = c->next) {
 		if ((c->callback == callback) && (c->priv == priv)) {
-			*p = next;
-			free(c);
+			c->removed = true;
 			return ERROR_OK;
-		} else
-			p = &(c->next);
-		c = next;
+		}
 	}
 
-	return ERROR_OK;
+	return ERROR_FAIL;
 }
 
 int target_call_event_callbacks(struct target *target, enum target_event event)
@@ -1522,31 +1517,44 @@ static int target_call_timer_callback(struct target_timer_callback *cb,
 
 static int target_call_timer_callbacks_check_time(int checktime)
 {
+	static bool callback_processing;
+
+	/* Do not allow nesting */
+	if (callback_processing)
+		return ERROR_OK;
+
+	callback_processing = true;
+
 	keep_alive();
 
 	struct timeval now;
 	gettimeofday(&now, NULL);
 
-	struct target_timer_callback *callback = target_timer_callbacks;
-	while (callback) {
-		/* cleaning up may unregister and free this callback */
-		struct target_timer_callback *next_callback = callback->next;
-
-		bool call_it = callback->callback &&
-			((!checktime && callback->periodic) ||
-			  now.tv_sec > callback->when.tv_sec ||
-			 (now.tv_sec == callback->when.tv_sec &&
-			  now.tv_usec >= callback->when.tv_usec));
-
-		if (call_it) {
-			int retval = target_call_timer_callback(callback, &now);
-			if (retval != ERROR_OK)
-				return retval;
+	/* Store an address of the place containing a pointer to the
+	 * next item; initially, that's a standalone "root of the
+	 * list" variable. */
+	struct target_timer_callback **callback = &target_timer_callbacks;
+	while (*callback) {
+		if ((*callback)->removed) {
+			struct target_timer_callback *p = *callback;
+			*callback = (*callback)->next;
+			free(p);
+			continue;
 		}
 
-		callback = next_callback;
+		bool call_it = (*callback)->callback &&
+			((!checktime && (*callback)->periodic) ||
+			 now.tv_sec > (*callback)->when.tv_sec ||
+			 (now.tv_sec == (*callback)->when.tv_sec &&
+			  now.tv_usec >= (*callback)->when.tv_usec));
+
+		if (call_it)
+			target_call_timer_callback(*callback, &now);
+
+		callback = &(*callback)->next;
 	}
 
+	callback_processing = false;
 	return ERROR_OK;
 }
 

src/target/target.h

@@ -294,6 +294,7 @@ struct target_timer_callback {
 	int (*callback)(void *priv);
 	int time_ms;
 	int periodic;
+	bool removed;
 	struct timeval when;
 	void *priv;
 	struct target_timer_callback *next;