[PATCH 3.16 020/212] hv: vmbus_post_msg: retry the hypercall on some transient errors

[Ben Hutchings]

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dexuan Cui <decui@xxxxxxxxxxxxx>

commit 89f9f6796d41e10e224b0cb0027ddd78cb881f65 upstream.

I got HV_STATUS_INVALID_CONNECTION_ID on Hyper-V 2008 R2 when keeping running
"rmmod hv_netvsc; modprobe hv_netvsc; rmmod hv_utils; modprobe hv_utils"
in a Linux guest. Looks the host has some kind of throttling mechanism if
some kinds of hypercalls are sent too frequently.
Without the patch, the driver can occasionally fail to load.

Also let's retry HV_STATUS_INSUFFICIENT_MEMORY, though we didn't get it
before.

Removed 'case -ENOMEM', since the hypervisor doesn't return this.

CC: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Reviewed-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/include/uapi/asm/hyperv.h |  2 ++
 drivers/hv/connection.c            | 11 +++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

--- a/arch/x86/include/uapi/asm/hyperv.h
+++ b/arch/x86/include/uapi/asm/hyperv.h
@@ -214,6 +214,8 @@
 #define HV_STATUS_INVALID_HYPERCALL_CODE	2
 #define HV_STATUS_INVALID_HYPERCALL_INPUT	3
 #define HV_STATUS_INVALID_ALIGNMENT		4
+#define HV_STATUS_INSUFFICIENT_MEMORY		11
+#define HV_STATUS_INVALID_CONNECTION_ID		18
 #define HV_STATUS_INSUFFICIENT_BUFFERS		19
 
 typedef struct _HV_REFERENCE_TSC_PAGE {
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -431,9 +431,16 @@ int vmbus_post_msg(void *buffer, size_t
 		ret = hv_post_message(conn_id, 1, buffer, buflen);
 
 		switch (ret) {
+		case HV_STATUS_INVALID_CONNECTION_ID:
+			/*
+			 * We could get this if we send messages too
+			 * frequently.
+			 */
+			ret = -EAGAIN;
+			break;
+		case HV_STATUS_INSUFFICIENT_MEMORY:
 		case HV_STATUS_INSUFFICIENT_BUFFERS:
 			ret = -ENOMEM;
-		case -ENOMEM:
 			break;
 		case HV_STATUS_SUCCESS:
 			return ret;
@@ -443,7 +450,7 @@ int vmbus_post_msg(void *buffer, size_t
 		}
 
 		retries++;
-		msleep(100);
+		msleep(1000);
 	}
 	return ret;
 }