From 379c83fa345444b696b5ab96f55ef55a18a9f309 Mon Sep 17 00:00:00 2001
From: Frank Pan <frankpzh@xxxxxxxxx>
Date: Wed, 2 Mar 2011 17:52:52 +0800
Subject: [PATCH] Use timeout on xenstore read_reply to avoid task hunging.

---
 linux-2.6-xen/drivers/xen/xenbus/xenbus_xs.c |   57 ++++++++++++++++++-------
 1 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/linux-2.6-xen/drivers/xen/xenbus/xenbus_xs.c b/linux-2.6-xen/drivers/xen/xenbus/xenbus_xs.c
index 5534690..4e66b30 100644
--- a/linux-2.6-xen/drivers/xen/xenbus/xenbus_xs.c
+++ b/linux-2.6-xen/drivers/xen/xenbus/xenbus_xs.c
@@ -73,6 +73,9 @@ struct xs_handle {
 	spinlock_t reply_lock;
 	wait_queue_head_t reply_waitq;
 
+	/* Sequence number of last request */
+	uint32_t reply_seq;
+
 	/*
 	 * Mutex ordering: transaction_mutex -> watch_mutex -> request_mutex.
 	 * response_mutex is never taken simultaneously with the other three.
@@ -136,26 +139,45 @@ static int get_error(const char *errorstring)
 	return xsd_errors[i].errnum;
 }
 
-static void *read_reply(enum xsd_sockmsg_type *type, unsigned int *len)
+#define XENSTORE_TIMEOUT (5*HZ)
+
+static void *read_reply(enum xsd_sockmsg_type *type, unsigned int *len, uint32_t seq)
 {
-	struct xs_stored_msg *msg;
+	unsigned long remain_time = XENSTORE_TIMEOUT;
+	struct xs_stored_msg *msg = 0;
 	char *body;
 
-	spin_lock(&xs_state.reply_lock);
-
-	while (list_empty(&xs_state.reply_list)) {
-		spin_unlock(&xs_state.reply_lock);
+	while (remain_time && !msg) {
 		/* XXX FIXME: Avoid synchronous wait for response here. */
-		wait_event(xs_state.reply_waitq,
-			   !list_empty(&xs_state.reply_list));
+		remain_time = wait_event_timeout(xs_state.reply_waitq,
+						 !list_empty(&xs_state.reply_list),
+						 remain_time);
+
 		spin_lock(&xs_state.reply_lock);
-	}
 
-	msg = list_entry(xs_state.reply_list.next,
-			 struct xs_stored_msg, list);
-	list_del(&msg->list);
+		while (!list_empty(&xs_state.reply_list)) {
+			msg = list_entry(xs_state.reply_list.next,
+					 struct xs_stored_msg, list);
+			list_del(&msg->list);
+
+			/* Check sequence number */
+			if (msg->hdr.req_id == seq)
+				break;
 
-	spin_unlock(&xs_state.reply_lock);
+			if (!IS_ERR(msg->u.reply.body))
+				kfree(msg->u.reply.body);
+			kfree(msg);
+			msg = 0;
+		}
+
+		spin_unlock(&xs_state.reply_lock);
+	}
+
+	if (!msg) {
+		*type = XS_ERROR;
+		*len = 0;
+		return ERR_PTR(-EIO);
+	}
 
 	*type = msg->hdr.type;
 	if (len)
@@ -202,13 +224,14 @@ void *xenbus_dev_request_and_reply(struct xsd_sockmsg *msg)
 		transaction_start();
 
 	mutex_lock(&xs_state.request_mutex);
+	msg->req_id = xs_state.reply_seq++;
 
 	err = xb_write(msg, sizeof(*msg) + msg->len);
 	if (err) {
 		msg->type = XS_ERROR;
 		ret = ERR_PTR(err);
 	} else
-		ret = read_reply(&msg->type, &msg->len);
+		ret = read_reply(&msg->type, &msg->len, msg->req_id);
 
 	mutex_unlock(&xs_state.request_mutex);
 
@@ -234,13 +257,13 @@ static void *xs_talkv(struct xenbus_transaction t,
 	int err;
 
 	msg.tx_id = t.id;
-	msg.req_id = 0;
 	msg.type = type;
 	msg.len = 0;
 	for (i = 0; i < num_vecs; i++)
 		msg.len += iovec[i].iov_len;
 
 	mutex_lock(&xs_state.request_mutex);
+	msg.req_id = xs_state.reply_seq++;
 
 	err = xb_write(&msg, sizeof(msg));
 	if (err) {
@@ -256,7 +279,7 @@ static void *xs_talkv(struct xenbus_transaction t,
 		}
 	}
 
-	ret = read_reply(&msg.type, len);
+	ret = read_reply(&msg.type, len, msg.req_id);
 
 	mutex_unlock(&xs_state.request_mutex);
 
@@ -872,6 +895,8 @@ int xs_init(void)
 	int err;
 	struct task_struct *task;
 
+	xs_state.reply_seq = 0;
+
 	INIT_LIST_HEAD(&xs_state.reply_list);
 	spin_lock_init(&xs_state.reply_lock);
 	init_waitqueue_head(&xs_state.reply_waitq);
-- 
1.7.1