Staging: hv: vmbus: Retry vmbus_post_msg() before giving up

The function hv_post_msg() can fail because of transient resource
conditions. It may be useful to retry the operation.
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

arch/x86/include/asm/hyperv.h

@@ -189,5 +189,6 @@
 #define HV_STATUS_INVALID_HYPERCALL_CODE	2
 #define HV_STATUS_INVALID_HYPERCALL_INPUT	3
 #define HV_STATUS_INVALID_ALIGNMENT		4
+#define HV_STATUS_INSUFFICIENT_BUFFERS		19
 
 #endif

drivers/staging/hv/connection.c

@@ -25,6 +25,7 @@
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
+#include <linux/delay.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
@@ -268,10 +269,25 @@ void vmbus_on_event(unsigned long data)
 int vmbus_post_msg(void *buffer, size_t buflen)
 {
 	union hv_connection_id conn_id;
+	int ret = 0;
+	int retries = 0;
 
 	conn_id.asu32 = 0;
 	conn_id.u.id = VMBUS_MESSAGE_CONNECTION_ID;
-	return hv_post_message(conn_id, 1, buffer, buflen);
+
+	/*
+	 * hv_post_message() can have transient failures because of
+	 * insufficient resources. Retry the operation a couple of
+	 * times before giving up.
+	 */
+	while (retries < 3) {
+		ret =  hv_post_message(conn_id, 1, buffer, buflen);
+		if (ret != HV_STATUS_INSUFFICIENT_BUFFERS)
+			return ret;
+		retries++;
+		msleep(100);
+	}
+	return ret;
 }
 
 /*