Drivers: hv: kvp,vss: Fast propagation of userspace communication failure

If we fail to send a message to userspace daemon with cn_netlink_send()
there is no need to wait for userspace to reply as it is not going to
happen. This happens when kvp or vss daemon is stopped after a successful
handshake. Report HV_E_FAIL immediately and cancel the timeout job so
host won't receive two failures.
Use pr_warn() for VSS and pr_debug() for KVP deliberately as VSS request
are rare and result in a failed backup. KVP requests are much more frequent
after a successful handshake so avoid flooding logs. It would be nice to
have an ability to de-negotiate with the host in case userspace daemon gets
disconnected so we won't receive new requests. But I'm not sure it is
possible.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 15 insertions, 2 deletions

diff --git a/drivers/hv/hv_kvp.c b/drivers/hv/hv_kvp.c
index 521c14625b3a..beb8105c0e7b 100644
--- a/drivers/hv/hv_kvp.c
+++ b/drivers/hv/hv_kvp.c
@@ -350,6 +350,7 @@ kvp_send_key(struct work_struct *dummy)
         __u8 pool = kvp_transaction.kvp_msg->kvp_hdr.pool;
         __u32 val32;
         __u64 val64;
+        int rc;
 
         msg = kzalloc(sizeof(*msg) + sizeof(struct hv_kvp_msg) , GFP_ATOMIC);
         if (!msg)
@@ -446,7 +447,13 @@ kvp_send_key(struct work_struct *dummy)
         }
 
         msg->len = sizeof(struct hv_kvp_msg);
-        cn_netlink_send(msg, 0, 0, GFP_ATOMIC);
+        rc = cn_netlink_send(msg, 0, 0, GFP_ATOMIC);
+        if (rc) {
+                pr_debug("KVP: failed to communicate to the daemon: %d\n", rc);
+                if (cancel_delayed_work_sync(&kvp_work))
+                        kvp_respond_to_host(message, HV_E_FAIL);
+        }
+
         kfree(msg);
 
         return;
diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index 21e51be74e6c..9d5e0d1efdb5 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -96,6 +96,7 @@ vss_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
 static void vss_send_op(struct work_struct *dummy)
 {
         int op = vss_transaction.msg->vss_hdr.operation;
+        int rc;
         struct cn_msg *msg;
         struct hv_vss_msg *vss_msg;
 
@@ -111,7 +112,12 @@ static void vss_send_op(struct work_struct *dummy)
         vss_msg->vss_hdr.operation = op;
         msg->len = sizeof(struct hv_vss_msg);
 
-        cn_netlink_send(msg, 0, 0, GFP_ATOMIC);
+        rc = cn_netlink_send(msg, 0, 0, GFP_ATOMIC);
+        if (rc) {
+                pr_warn("VSS: failed to communicate to the daemon: %d\n", rc);
+                if (cancel_delayed_work_sync(&vss_timeout_work))
+                        vss_respond_to_host(HV_E_FAIL);
+        }
         kfree(msg);
 
         return;