[PATCH 2/3] hv: vmbus_post_msg: retry the hypercall on HV_STATUS_INVALID_CONNECTION_ID

[Dexuan Cui <decui@microsoft.com>]

I got the hypercall error code on Hyper-V 2008 R2 when keeping running
"rmmod hv_netvsc; modprobe hv_netvsc; rmmod hv_utils; modprobe hv_utils"
in a Linux guest.

Without the patch, the driver can occasionally fail to load.

CC: "K. Y. Srinivasan" <kys@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 arch/x86/include/uapi/asm/hyperv.h | 1 +
 drivers/hv/connection.c            | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/arch/x86/include/uapi/asm/hyperv.h b/arch/x86/include/uapi/asm/hyperv.h
index 90c458e..b9daffb 100644
--- a/arch/x86/include/uapi/asm/hyperv.h
+++ b/arch/x86/include/uapi/asm/hyperv.h
@@ -225,6 +225,7 @@
 #define HV_STATUS_INVALID_HYPERCALL_CODE	2
 #define HV_STATUS_INVALID_HYPERCALL_INPUT	3
 #define HV_STATUS_INVALID_ALIGNMENT		4
+#define HV_STATUS_INVALID_CONNECTION_ID		18
 #define HV_STATUS_INSUFFICIENT_BUFFERS		19
 
 typedef struct _HV_REFERENCE_TSC_PAGE {
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index c4acd1c..8bd05f3 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -440,6 +440,15 @@ int vmbus_post_msg(void *buffer, size_t buflen)
 		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 or the host is under low resource
+			 * conditions: let's wait 1 more second before
+			 * retrying the hypercall.
+			 */
+			msleep(1000);
+			break;
 		case HV_STATUS_INSUFFICIENT_BUFFERS:
 			ret = -ENOMEM;
 		case -ENOMEM:
-- 
1.9.1