svn commit: r255714 - head/sbin/hastd

[Mikolaj Golub]

Author: trociny
Date: Thu Sep 19 20:15:24 2013
New Revision: 255714
URL: http://svnweb.freebsd.org/changeset/base/255714

Log:
  Use cv_broadcast() instead of cv_signal() when waking up threads
  waiting on an empty queue as the queue may have several consumers.
  
  Before the fix the following scenario was possible: 2 threads are
  waiting on empty queue, 2 threads are inserting simultaneously. The
  first inserting thread detects that the queue is empty and is going to
  send the signal, but before it sends the second thread inserts
  too. When the first sends the signal only one of the waiting threads
  receive it while the other one may wait forever.
  
  The scenario above is is believed to be the cause of the observed
  cases, when ggate_recv_thread() was getting stuck on taking free
  request, while the free queue was not empty.
  
  Reviewed by:	pjd
  Tested by:	Yamagi Burmeister yamagi.org
  Approved by:	re (marius)
  MFC after:	2 weeks

Modified:
  head/sbin/hastd/primary.c
  head/sbin/hastd/secondary.c

Modified: head/sbin/hastd/primary.c
==============================================================================
--- head/sbin/hastd/primary.c	Thu Sep 19 20:09:56 2013	(r255713)
+++ head/sbin/hastd/primary.c	Thu Sep 19 20:15:24 2013	(r255714)
@@ -172,7 +172,7 @@ static pthread_mutex_t metadata_lock;
 	    hio_next[(ncomp)]);						\
 	mtx_unlock(&hio_##name##_list_lock[ncomp]);			\
 	if (_wakeup)							\
-		cv_signal(&hio_##name##_list_cond[(ncomp)]);		\
+		cv_broadcast(&hio_##name##_list_cond[(ncomp)]);		\
 } while (0)
 #define	QUEUE_INSERT2(hio, name)	do {				\
 	bool _wakeup;							\
@@ -182,7 +182,7 @@ static pthread_mutex_t metadata_lock;
 	TAILQ_INSERT_TAIL(&hio_##name##_list, (hio), hio_##name##_next);\
 	mtx_unlock(&hio_##name##_list_lock);				\
 	if (_wakeup)							\
-		cv_signal(&hio_##name##_list_cond);			\
+		cv_broadcast(&hio_##name##_list_cond);			\
 } while (0)
 #define	QUEUE_TAKE1(hio, name, ncomp, timeout)	do {			\
 	bool _last;							\

Modified: head/sbin/hastd/secondary.c
==============================================================================
--- head/sbin/hastd/secondary.c	Thu Sep 19 20:09:56 2013	(r255713)
+++ head/sbin/hastd/secondary.c	Thu Sep 19 20:15:24 2013	(r255714)
@@ -115,7 +115,7 @@ static void *send_thread(void *arg);
 	TAILQ_INSERT_TAIL(&hio_##name##_list, (hio), hio_next);		\
 	mtx_unlock(&hio_##name##_list_lock);				\
 	if (_wakeup)							\
-		cv_signal(&hio_##name##_list_cond);			\
+		cv_broadcast(&hio_##name##_list_cond);			\
 } while (0)
 #define	QUEUE_TAKE(name, hio)	do {					\
 	mtx_lock(&hio_##name##_list_lock);				\