Merge lp:~laurynas-biveinis/percona-server/bug1235285 into lp:percona-server/5.6

[Laurynas Biveinis]

Fix bug 1235285 (Missed wakeup events in priority rw lock).

The following issues were found and addressed.
- high_priority_wait_ex_waiter was never set, meaning, that a sole
high-priority X waiter coming after any S waits will not receive its
wakeup event. Fixed by adding high_priority flag arg to
rw_lock_x_lock_wait() and setting high_priority_wait_ex_waiter there
as needed.

- Since low-priority S acquisitions were made to wait instead of
acquire when a high-priority S lockers exist, it is possible to have
waiters on S releases now. This was not done before, and fixed by
adjusting rw_lock_s_unlock_func() to set the regular RW lock event on
S unlocks too if needed.

http://jenkins.percona.com/job/percona-server-5.6-param/355/

[Sergei Glushchenko (sergei.glushchenko)]

Approve

review: Approve (g2)

=== modified file 'Percona-Server/storage/innobase/include/sync0rw.ic'
--- Percona-Server/storage/innobase/include/sync0rw.ic	2013-09-26 14:58:37 +0000
+++ Percona-Server/storage/innobase/include/sync0rw.ic	2013-10-04 17:55:53 +0000
@@ -604,6 +604,8 @@
 #endif
 	prio_rw_lock_t*	lock)	/*!< in/out: rw-lock */
 {
+	lint lock_word;
+
 	ut_ad(lock->base_lock.lock_word > -X_LOCK_DECR);
 	ut_ad(lock->base_lock.lock_word != 0);
 	ut_ad(lock->base_lock.lock_word < X_LOCK_DECR);
@@ -613,7 +615,8 @@
 #endif
 
 	/* Increment lock_word to indicate 1 less reader */
-	if (rw_lock_lock_word_incr(&lock->base_lock, 1) == 0) {
+	lock_word = rw_lock_lock_word_incr(&lock->base_lock, 1);
+	if (lock_word == 0) {
 
 		/* A waiting next-writer exists, either high priority or
 		regular.  Wake up the first waiter in this order: 1) high
@@ -642,6 +645,17 @@
 			os_event_set(lock->base_lock.wait_ex_event);
 		}
 		sync_array_object_signalled();
+	} else if (lock_word == X_LOCK_DECR) {
+
+		/* S-waiters may exist during an S unlock if a high-priority
+		thread released it, because low-priority threads are prevented
+		from acquiring S lock while high-priority thread holds it.  */
+		if (lock->base_lock.waiters) {
+
+			rw_lock_reset_waiter_flag(&lock->base_lock);
+			os_event_set(lock->base_lock.event);
+			sync_array_object_signalled();
+		}
 	}
 
 	ut_ad(rw_lock_validate(lock));

=== modified file 'Percona-Server/storage/innobase/sync/sync0rw.cc'
--- Percona-Server/storage/innobase/sync/sync0rw.cc	2013-09-26 14:58:37 +0000
+++ Percona-Server/storage/innobase/sync/sync0rw.cc	2013-10-04 17:55:53 +0000
@@ -569,6 +569,10 @@
 rw_lock_x_lock_wait(
 /*================*/
 	rw_lock_t*	lock,	/*!< in: pointer to rw-lock */
+	bool		high_priority,
+				/*!< in: if true, the rw lock is a priority
+				lock and is being acquired with high
+				priority  */
 #ifdef UNIV_SYNC_DEBUG
 	ulint		pass,	/*!< in: pass value; != 0, if the lock will
 				be passed to another thread to unlock */
@@ -606,6 +610,13 @@
 			sync_arr, lock, RW_LOCK_WAIT_EX,
 			file_name, line, &index);
 
+		if (high_priority) {
+
+			prio_rw_lock_t*	prio_rw_lock
+				= reinterpret_cast<prio_rw_lock_t *>(lock);
+			prio_rw_lock->high_priority_wait_ex_waiter = 1;
+		}
+
 		i = 0;
 
 		/* Check lock_word to ensure wake-up isn't missed.*/
@@ -645,6 +656,10 @@
 rw_lock_x_lock_low(
 /*===============*/
 	rw_lock_t*	lock,	/*!< in: pointer to rw-lock */
+	bool		high_priority,
+				/*!< in: if true, the rw lock is a priority
+			        lock and is being acquired with high
+				priority  */
 	ulint		pass,	/*!< in: pass value; != 0, if the lock will
 				be passed to another thread to unlock */
 	const char*	file_name,/*!< in: file name where lock requested */
@@ -662,7 +677,7 @@
 		rw_lock_set_writer_id_and_recursion_flag(
 			lock, pass ? FALSE : TRUE);
 
-		rw_lock_x_lock_wait(lock,
+		rw_lock_x_lock_wait(lock, high_priority,
 #ifdef UNIV_SYNC_DEBUG
 				    pass,
 #endif
@@ -737,11 +752,14 @@
 
 	i = 0;
 
+	ut_ad(priority_lock || !high_priority);
+
 lock_loop:
 
 	if (!rw_lock_higher_prio_waiters_exist(priority_lock, high_priority,
 					       lock)
-	    && rw_lock_x_lock_low(lock, pass, file_name, line)) {
+	    && rw_lock_x_lock_low(lock, high_priority, pass,
+				  file_name, line)) {
 		rw_lock_stats.rw_x_spin_round_count.add(counter_index, i);
 
 		return;	/* Locking succeeded */
@@ -808,7 +826,7 @@
 		rw_lock_set_waiter_flag(lock);
 	}
 
-	if (rw_lock_x_lock_low(lock, pass, file_name, line)) {
+	if (rw_lock_x_lock_low(lock, high_priority, pass, file_name, line)) {
 		sync_array_free_cell(sync_arr, index);
 		return; /* Locking succeeded */
 	}