RE: [PATCH] Drivers: hv: util: on deinit, don't wait the release event, if we shouldn't

[Stephen Hemminger]

The patch looks good. I don't  understand the exact semantics here and therefore have a couple of naïve questions

Is it possible device could be opened multiple times? Is reference counting done above?
If device was never opened do you even have to do all the cleanup steps at all?

-----Original Message-----
From: Dexuan Cui 
Sent: Monday, February 27, 2017 3:26 AM
To: gregkh@xxxxxxxxxxxxxxxxxxx; driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx; KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; Alex Ng (LIS) <alexng@xxxxxxxxxxxxx>
Subject: [PATCH] Drivers: hv: util: on deinit, don't wait the release event, if we shouldn't


If the daemon is NOT running at all, when we disable the util device from
Hyper-V Manager (or sometimes the host can rescind a util device and then
re-offer it), we'll hang in util_remove -> hv_kvp_deinit ->
wait_for_completion(&release_event), because this code path doesn't run:
hvt_op_release -> ... -> kvp_on_reset -> complete(&release_event).

Due to this, we even can't reboot the VM properly.

The patch tracks if the dev file is opened or not, and we only need to
wait if it's opened.

Fixes: 5a66fecbf6aa ("Drivers: hv: util: kvp: Fix a rescind processing issue")
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
---
 drivers/hv/hv_fcopy.c           | 5 ++++-
 drivers/hv/hv_kvp.c             | 6 +++++-
 drivers/hv/hv_snapshot.c        | 5 ++++-
 drivers/hv/hv_utils_transport.c | 2 ++
 drivers/hv/hv_utils_transport.h | 1 +
 5 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
index 9aee601..545cf43 100644
--- a/drivers/hv/hv_fcopy.c
+++ b/drivers/hv/hv_fcopy.c
@@ -358,8 +358,11 @@ int hv_fcopy_init(struct hv_util_service *srv)
 
 void hv_fcopy_deinit(void)
 {
+	bool wait = hvt->dev_opened;
+
 	fcopy_transaction.state = HVUTIL_DEVICE_DYING;
 	cancel_delayed_work_sync(&fcopy_timeout_work);
 	hvutil_transport_destroy(hvt);
-	wait_for_completion(&release_event);
+	if (wait)
+		wait_for_completion(&release_event);
 }
diff --git a/drivers/hv/hv_kvp.c b/drivers/hv/hv_kvp.c
index de26371..15c7873 100644
--- a/drivers/hv/hv_kvp.c
+++ b/drivers/hv/hv_kvp.c
@@ -742,10 +742,14 @@ hv_kvp_init(struct hv_util_service *srv)
 
 void hv_kvp_deinit(void)
 {
+	bool wait = hvt->dev_opened;
+
 	kvp_transaction.state = HVUTIL_DEVICE_DYING;
 	cancel_delayed_work_sync(&kvp_host_handshake_work);
 	cancel_delayed_work_sync(&kvp_timeout_work);
 	cancel_work_sync(&kvp_sendkey_work);
 	hvutil_transport_destroy(hvt);
-	wait_for_completion(&release_event);
+
+	if (wait)
+		wait_for_completion(&release_event);
 }
diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index bcc03f0..3847f19 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -396,9 +396,12 @@ hv_vss_init(struct hv_util_service *srv)
 
 void hv_vss_deinit(void)
 {
+	bool wait = hvt->dev_opened;
+
 	vss_transaction.state = HVUTIL_DEVICE_DYING;
 	cancel_delayed_work_sync(&vss_timeout_work);
 	cancel_work_sync(&vss_handle_request_work);
 	hvutil_transport_destroy(hvt);
-	wait_for_completion(&release_event);
+	if (wait)
+		wait_for_completion(&release_event);
 }
diff --git a/drivers/hv/hv_utils_transport.c b/drivers/hv/hv_utils_transport.c
index c235a95..05e0648 100644
--- a/drivers/hv/hv_utils_transport.c
+++ b/drivers/hv/hv_utils_transport.c
@@ -153,6 +153,7 @@ static int hvt_op_open(struct inode *inode, struct file *file)
 
 	if (issue_reset)
 		hvt_reset(hvt);
+	hvt->dev_opened = (hvt->mode == HVUTIL_TRANSPORT_CHARDEV) && !ret;
 
 	mutex_unlock(&hvt->lock);
 
@@ -182,6 +183,7 @@ static int hvt_op_release(struct inode *inode, struct file *file)
 	 * connects back.
 	 */
 	hvt_reset(hvt);
+	hvt->dev_opened = false;
 	mutex_unlock(&hvt->lock);
 
 	if (mode_old == HVUTIL_TRANSPORT_DESTROY)
diff --git a/drivers/hv/hv_utils_transport.h b/drivers/hv/hv_utils_transport.h
index d98f522..9871283 100644
--- a/drivers/hv/hv_utils_transport.h
+++ b/drivers/hv/hv_utils_transport.h
@@ -32,6 +32,7 @@ struct hvutil_transport {
 	int mode;                           /* hvutil_transport_mode */
 	struct file_operations fops;        /* file operations */
 	struct miscdevice mdev;             /* misc device */
+	bool   dev_opened;                  /* Is the device opened? */
 	struct cb_id cn_id;                 /* CN_*_IDX/CN_*_VAL */
 	struct list_head list;              /* hvt_list */
 	int (*on_msg)(void *, int);         /* callback on new user message */
-- 
2.7.4