hv: run non-blocking message handlers in the dispatch tasklet

A work item in vmbus_connection.work_queue can sleep, waiting for a new
host message (usually it is some kind of "completion" message). Currently
the new message will be handled in the same workqueue, but since work items
in the workqueue is serialized, we actually have no chance to handle
the new message if the current work item is sleeping -- as as result, the
current work item will hang forever.

K. Y. has posted the below fix to resolve the issue:
Drivers: hv: vmbus: Perform device register in the per-channel work element

Actually we can simplify the fix by directly running non-blocking message
handlers in the dispatch tasklet (inspired by K. Y.).

This patch is the fundamental change. The following 2 patches will simplify
the message offering and rescind-offering handling a lot.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index c8e27e0..f40a5a9 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -685,6 +685,23 @@ struct vmbus_msginfo {
 
 extern struct vmbus_connection vmbus_connection;
 
+enum vmbus_message_handler_type {
+	/* The related handler can sleep. */
+	VMHT_BLOCKING = 0,
+
+	/* The related handler must NOT sleep. */
+	VMHT_NON_BLOCKING = 1,
+};
+
+struct vmbus_channel_message_table_entry {
+	enum vmbus_channel_message_type message_type;
+	enum vmbus_message_handler_type handler_type;
+	void (*message_handler)(struct vmbus_channel_message_header *msg);
+};
+
+extern struct vmbus_channel_message_table_entry
+	channel_message_table[CHANNELMSG_COUNT];
+
 /* General vmbus interface */
 
 struct hv_device *vmbus_device_create(const uuid_le *type,