[PATCH v2] hv: retry infinitely on hypercall transient failures

Long Li
2017-01-05T00:15:31Z

From: Long Li <longli@microsoft.com>

Hyper-v host guarantees that a hypercall will finish in reasonable time.
Retry infinitely on transient failures to avoid returning error to upper layer.

Signed-off-by: Long Li <longli@microsoft.com>
---
drivers/hv/connection.c | 30 ++++++++++++++----------------
1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 6ce8b87..4b3cfde 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -438,46 +438,44 @@ 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;
+ int ret;
u32 usec = 1;

conn_id.asu32 = 0;
conn_id.u.id = VMBUS_MESSAGE_CONNECTION_ID;

/*
- * hv_post_message() can have transient failures because of
- * insufficient resources. Retry the operation a couple of
- * times before giving up.
+ * hv_post_message() can have transient failures. We retry infinitely
+ * on these failures because host guarantees hypercall will finish.
*/
- while (retries < 20) {
+ while (1) {
ret = hv_post_message(conn_id, 1, buffer, buflen);

switch (ret) {
+ /*
+ * Retry on transient failures:
+ * 1. HV_STATUS_INVALID_CONNECTION_ID:
+ * We send messages too frequently.
+ *
+ * 2. HV_STATUS_INSUFFICIENT_MEMORY and
+ * HV_STATUS_INSUFFICIENT_BUFFERS:
+ * The host is temporariliy running out of resources.
+ */
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;
break;
case HV_STATUS_SUCCESS:
- return ret;
+ return 0;
default:
pr_err("hv_post_msg() failed; error code:%d\n", ret);
return -EINVAL;
}

- retries++;
udelay(usec);
if (usec < 2048)
usec *= 2;
}
- return ret;
}

/*
--
2.7.4