2489. [port] solaris: Workaround Solaris's kernel bug about

/dev/poll:
			http://bugs.opensolaris.org/view_bug.do?bug_id=6724237
			Define ISC_SOCKET_USE_POLLWATCH at build time to enable
			this workaround. [RT #18870]

CHANGES

@@ -1,3 +1,9 @@
+2489.	[port]		solaris: Workaround Solaris's kernel bug about
+			/dev/poll:
+			http://bugs.opensolaris.org/view_bug.do?bug_id=6724237
+			Define ISC_SOCKET_USE_POLLWATCH at build time to enable
+			this workaround. [RT #18870]
+
 2488.	[func]		Added a tool, dnssec-dsfromkey, to generate DS records
 			from keyset and .key files. [RT #18694]
 

README

@@ -457,6 +457,10 @@ Building
 		To create the default pid files in ${localstatedir}/run rather
 		than ${localstatedir}/run/{named,lwresd}/ set.
 		  -DNS_RUN_PID_DIR=0
+		Enabling workaround for Solaris kernel bug about /dev/poll
+		  -DISC_SOCKET_USE_POLLWATCH=1
+		  The watch timeout is also configurable, e.g.,
+		  -DISC_SOCKET_POLLWATCH_TIMEOUT=20
 
 	    LDFLAGS
 		Linker flags. Defaults to empty string.

lib/isc/unix/socket.c

@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: socket.c,v 1.304 2008/10/17 21:49:23 jinmei Exp $ */
+/* $Id: socket.c,v 1.305 2008/11/08 22:35:12 jinmei Exp $ */
 
 /*! \file */
 
@@ -148,6 +148,35 @@ struct isc_socketwait {
 #endif	/* __APPLE__ */
 #endif	/* USE_SELECT */
 
+#ifdef ISC_SOCKET_USE_POLLWATCH
+/*%
+ * If this macro is defined, enable workaround for a Solaris /dev/poll kernel
+ * bug: DP_POLL ioctl could keep sleeping even if socket I/O is possible for
+ * some of the specified FD.  The idea is based on the observation that it's
+ * likely for a busy server to keep receiving packets.  It specifically works
+ * as follows: the socket watcher is first initialized with the state of
+ * "poll_idle".  While it's in the idle state it keeps sleeping until a socket
+ * event occurs.  When it wakes up for a socket I/O event, it moves to the
+ * poll_active state, and sets the poll timeout to a short period
+ * (ISC_SOCKET_POLLWATCH_TIMEOUT msec).  If timeout occurs in this state, the
+ * watcher goes to the poll_checking state with the same timeout period.
+ * In this state, the watcher tries to detect whether this is a break
+ * during intermittent events or the kernel bug is triggered.  If the next
+ * polling reports an event within the short period, the previous timeout is
+ * likely to be a kernel bug, and so the watcher goes back to the active state.
+ * Otherwise, it moves to the idle state again.
+ *
+ * It's not clear whether this is a thread-related bug, but since we've only
+ * seen this with threads, this workaround is used only when enabling threads.
+ */
+
+typedef enum { poll_idle, poll_active, poll_checking } pollstate_t;
+
+#ifndef ISC_SOCKET_POLLWATCH_TIMEOUT
+#define ISC_SOCKET_POLLWATCH_TIMEOUT 10
+#endif	/* ISC_SOCKET_POLLWATCH_TIMEOUT */
+#endif	/* ISC_SOCKET_USE_POLLWATCH */
+
 /*%
  * Size of per-FD lock buckets.
  */
@@ -3230,6 +3259,9 @@ watcher(void *uap) {
 	int maxfd;
 #endif
 	char strbuf[ISC_STRERRORSIZE];
+#ifdef ISC_SOCKET_USE_POLLWATCH
+	pollstate_t pollstate = poll_idle;
+#endif
 
 	/*
 	 * Get the control fd here.  This will never change.
@@ -3247,7 +3279,14 @@ watcher(void *uap) {
 #elif defined(USE_DEVPOLL)
 			dvp.dp_fds = manager->events;
 			dvp.dp_nfds = manager->nevents;
+#ifndef ISC_SOCKET_USE_POLLWATCH
 			dvp.dp_timeout = -1;
+#else
+			if (pollstate == poll_idle)
+				dvp.dp_timeout = -1;
+			else
+				dvp.dp_timeout = ISC_SOCKET_POLLWATCH_TIMEOUT;
+#endif	/* ISC_SOCKET_USE_POLLWATCH */
 			cc = ioctl(manager->devpoll_fd, DP_POLL, &dvp);
 #elif defined(USE_SELECT)
 			LOCK(&manager->lock);
@@ -3271,6 +3310,33 @@ watcher(void *uap) {
 							   ISC_MSG_FAILED,
 							   "failed"), strbuf);
 			}
+
+#if defined(USE_DEVPOLL) && defined(ISC_SOCKET_USE_POLLWATCH)
+			if (cc == 0) {
+				if (pollstate == poll_active)
+					pollstate = poll_checking;
+				else if (pollstate == poll_checking)
+					pollstate = poll_idle;
+			} else if (cc > 0) {
+				if (pollstate == poll_checking) {
+					/*
+					 * XXX: We'd like to use a more
+					 * verbose log level as it's actually an
+					 * unexpected event, but the kernel bug
+					 * reportedly happens pretty frequently
+					 * (and it can also be a false positive)
+					 * so it would be just too noisy.
+					 */
+					manager_log(manager,
+						    ISC_LOGCATEGORY_GENERAL,
+						    ISC_LOGMODULE_SOCKET,
+						    ISC_LOG_DEBUG(1),
+						    ISC_LOG_INFO,
+						    "unexpected POLL timeout");
+				}
+				pollstate = poll_active;
+			}
+#endif
 		} while (cc < 0);
 
 #if defined(USE_KQUEUE) || defined (USE_EPOLL) || defined (USE_DEVPOLL)