staging: lustre: replace l_wait_event_exclusive_head() with wait_event_idle_exclusive

This l_wait_event_exclusive_head() will wait indefinitely
if the timeout is zero.  If it does wait with a timeout
and times out, the timeout for next time is set to zero.

The can be mapped to a call to either
 wait_event_idle_exclusive()
or
 wait_event_idle_exclusive_timeout()
depending in the timeout setting.

The current code arranges for LIFO queuing of waiters,
but include/event.h doesn't support that yet.
Until it does, fall back on FIFO with
wait_event_idle_exclusive{,_timeout}().
Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/ptlrpc/service.c

@@ -1897,15 +1897,6 @@ ptlrpc_check_rqbd_pool(struct ptlrpc_service_part *svcpt)
 	}
 }
 
-static int
-ptlrpc_retry_rqbds(void *arg)
-{
-	struct ptlrpc_service_part *svcpt = arg;
-
-	svcpt->scp_rqbd_timeout = 0;
-	return -ETIMEDOUT;
-}
-
 static inline int
 ptlrpc_threads_enough(struct ptlrpc_service_part *svcpt)
 {
@@ -1968,13 +1959,17 @@ ptlrpc_server_request_incoming(struct ptlrpc_service_part *svcpt)
 	return !list_empty(&svcpt->scp_req_incoming);
 }
 
+/* We perfer lifo queuing, but kernel doesn't provide that yet. */
+#ifndef wait_event_idle_exclusive_lifo
+#define wait_event_idle_exclusive_lifo wait_event_idle_exclusive
+#define wait_event_idle_exclusive_lifo_timeout wait_event_idle_exclusive_timeout
+#endif
+
 static __attribute__((__noinline__)) int
 ptlrpc_wait_event(struct ptlrpc_service_part *svcpt,
 		  struct ptlrpc_thread *thread)
 {
 	/* Don't exit while there are replies to be handled */
-	struct l_wait_info lwi = LWI_TIMEOUT(svcpt->scp_rqbd_timeout,
-					     ptlrpc_retry_rqbds, svcpt);
 
 	/* XXX: Add this back when libcfs watchdog is merged upstream
 	lc_watchdog_disable(thread->t_watchdog);
@@ -1982,13 +1977,25 @@ ptlrpc_wait_event(struct ptlrpc_service_part *svcpt,
 
 	cond_resched();
 
-	l_wait_event_exclusive_head(svcpt->scp_waitq,
+	if (svcpt->scp_rqbd_timeout == 0)
+		wait_event_idle_exclusive_lifo(
+			svcpt->scp_waitq,
+			ptlrpc_thread_stopping(thread) ||
+			ptlrpc_server_request_incoming(svcpt) ||
+			ptlrpc_server_request_pending(svcpt,
+						      false) ||
+			ptlrpc_rqbd_pending(svcpt) ||
+			ptlrpc_at_check(svcpt));
+	else if (0 == wait_event_idle_exclusive_lifo_timeout(
+			 svcpt->scp_waitq,
 			 ptlrpc_thread_stopping(thread) ||
 			 ptlrpc_server_request_incoming(svcpt) ||
 			 ptlrpc_server_request_pending(svcpt,
 						       false) ||
 			 ptlrpc_rqbd_pending(svcpt) ||
-				    ptlrpc_at_check(svcpt), &lwi);
+			 ptlrpc_at_check(svcpt),
+			 svcpt->scp_rqbd_timeout))
+		svcpt->scp_rqbd_timeout = 0;
 
 	if (ptlrpc_thread_stopping(thread))
 		return -EINTR;