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

[Vitaly Kuznetsov <vkuznets@redhat.com>]

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Vitaly Kuznetsov <vkuznets@redhat.com> writes:

> Dexuan Cui <decui@microsoft.com> writes:
>
>>> From: devel [...] On Behalf Of Dexuan Cui
>>> > > --- 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 */
>>> >
>>> > I think we can get away without introducing this new flag, e.g. if we
>>> > replace release_event with an atomic which will hold the state
>>> > (open/closed). This will also elimenate possible races above. I can try
>>> > prototyping a patch if you want me to.
>>> > --
>>> >   Vitaly
>>> 
>>> Thanks for offering the help! Please do. :-)
>>
>> BTW, IMO I found another potential issue:
>> In hvt_op_open -> hvt_reset -> kvp_on_reset(), I think we should call
>> init_completion() instead of complete()?
>>
>
> To me it looks like we can do better with something different from
> struct completion, I'll take a look later today.

Dexuan,

please take a look at the attached patch. After looking at the code
again it occured to me that it's going to be easier to move release wait
to the transport itself. Lightly tested.

Thanks!

-- 
  Vitaly


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>From e1144c6127d4f9acffeb64f40449de365caec51e Mon Sep 17 00:00:00 2001
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Tue, 28 Feb 2017 15:12:17 +0100
Subject: [PATCH] Drivers: hv: util: move waiting for release to
 hv_utils_transport itself

Waiting for release_event in all three drivers introduced issues on release
as on_reset() hook is not always called. E.g. if the device was never
opened we will never get the completion.

Move the waiting code to hvutil_transport_destroy() and make sure it is
only called when the device is open. hvt->lock serialization should
guarantee the absence of races.

Fixes: 5a66fecbf6aa ("Drivers: hv: util: kvp: Fix a rescind processing issue")
Fixes: 20951c7535b5 ("Drivers: hv: util: Fcopy: Fix a rescind processing issue")
Fixes: d77044d142e9 ("Drivers: hv: util: Backup: Fix a rescind processing issue")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 drivers/hv/hv_fcopy.c           |  4 ----
 drivers/hv/hv_kvp.c             |  4 ----
 drivers/hv/hv_snapshot.c        |  4 ----
 drivers/hv/hv_utils_transport.c | 12 ++++++++----
 drivers/hv/hv_utils_transport.h |  1 +
 5 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
index 9aee601..a5596a6 100644
--- a/drivers/hv/hv_fcopy.c
+++ b/drivers/hv/hv_fcopy.c
@@ -71,7 +71,6 @@ static DECLARE_WORK(fcopy_send_work, fcopy_send_data);
 static const char fcopy_devname[] = "vmbus/hv_fcopy";
 static u8 *recv_buffer;
 static struct hvutil_transport *hvt;
-static struct completion release_event;
 /*
  * This state maintains the version number registered by the daemon.
  */
@@ -331,7 +330,6 @@ static void fcopy_on_reset(void)
 
 	if (cancel_delayed_work_sync(&fcopy_timeout_work))
 		fcopy_respond_to_host(HV_E_FAIL);
-	complete(&release_event);
 }
 
 int hv_fcopy_init(struct hv_util_service *srv)
@@ -339,7 +337,6 @@ int hv_fcopy_init(struct hv_util_service *srv)
 	recv_buffer = srv->recv_buffer;
 	fcopy_transaction.recv_channel = srv->channel;
 
-	init_completion(&release_event);
 	/*
 	 * When this driver loads, the user level daemon that
 	 * processes the host requests may not yet be running.
@@ -361,5 +358,4 @@ void hv_fcopy_deinit(void)
 	fcopy_transaction.state = HVUTIL_DEVICE_DYING;
 	cancel_delayed_work_sync(&fcopy_timeout_work);
 	hvutil_transport_destroy(hvt);
-	wait_for_completion(&release_event);
 }
diff --git a/drivers/hv/hv_kvp.c b/drivers/hv/hv_kvp.c
index de26371..a1adfe2 100644
--- a/drivers/hv/hv_kvp.c
+++ b/drivers/hv/hv_kvp.c
@@ -101,7 +101,6 @@ static DECLARE_WORK(kvp_sendkey_work, kvp_send_key);
 static const char kvp_devname[] = "vmbus/hv_kvp";
 static u8 *recv_buffer;
 static struct hvutil_transport *hvt;
-static struct completion release_event;
 /*
  * Register the kernel component with the user-level daemon.
  * As part of this registration, pass the LIC version number.
@@ -714,7 +713,6 @@ static void kvp_on_reset(void)
 	if (cancel_delayed_work_sync(&kvp_timeout_work))
 		kvp_respond_to_host(NULL, HV_E_FAIL);
 	kvp_transaction.state = HVUTIL_DEVICE_INIT;
-	complete(&release_event);
 }
 
 int
@@ -723,7 +721,6 @@ hv_kvp_init(struct hv_util_service *srv)
 	recv_buffer = srv->recv_buffer;
 	kvp_transaction.recv_channel = srv->channel;
 
-	init_completion(&release_event);
 	/*
 	 * When this driver loads, the user level daemon that
 	 * processes the host requests may not yet be running.
@@ -747,5 +744,4 @@ void hv_kvp_deinit(void)
 	cancel_delayed_work_sync(&kvp_timeout_work);
 	cancel_work_sync(&kvp_sendkey_work);
 	hvutil_transport_destroy(hvt);
-	wait_for_completion(&release_event);
 }
diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index bcc03f0..e659d1b 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -79,7 +79,6 @@ static int dm_reg_value;
 static const char vss_devname[] = "vmbus/hv_vss";
 static __u8 *recv_buffer;
 static struct hvutil_transport *hvt;
-static struct completion release_event;
 
 static void vss_timeout_func(struct work_struct *dummy);
 static void vss_handle_request(struct work_struct *dummy);
@@ -361,13 +360,11 @@ static void vss_on_reset(void)
 	if (cancel_delayed_work_sync(&vss_timeout_work))
 		vss_respond_to_host(HV_E_FAIL);
 	vss_transaction.state = HVUTIL_DEVICE_INIT;
-	complete(&release_event);
 }
 
 int
 hv_vss_init(struct hv_util_service *srv)
 {
-	init_completion(&release_event);
 	if (vmbus_proto_version < VERSION_WIN8_1) {
 		pr_warn("Integration service 'Backup (volume snapshot)'"
 			" not supported on this host version.\n");
@@ -400,5 +397,4 @@ void hv_vss_deinit(void)
 	cancel_delayed_work_sync(&vss_timeout_work);
 	cancel_work_sync(&vss_handle_request_work);
 	hvutil_transport_destroy(hvt);
-	wait_for_completion(&release_event);
 }
diff --git a/drivers/hv/hv_utils_transport.c b/drivers/hv/hv_utils_transport.c
index c235a95..4402a71 100644
--- a/drivers/hv/hv_utils_transport.c
+++ b/drivers/hv/hv_utils_transport.c
@@ -182,10 +182,11 @@ static int hvt_op_release(struct inode *inode, struct file *file)
 	 * connects back.
 	 */
 	hvt_reset(hvt);
-	mutex_unlock(&hvt->lock);
 
 	if (mode_old == HVUTIL_TRANSPORT_DESTROY)
-		hvt_transport_free(hvt);
+		complete(&hvt->release);
+
+	mutex_unlock(&hvt->lock);
 
 	return 0;
 }
@@ -304,6 +305,7 @@ struct hvutil_transport *hvutil_transport_init(const char *name,
 
 	init_waitqueue_head(&hvt->outmsg_q);
 	mutex_init(&hvt->lock);
+	init_completion(&hvt->release);
 
 	spin_lock(&hvt_list_lock);
 	list_add(&hvt->list, &hvt_list);
@@ -351,6 +353,8 @@ void hvutil_transport_destroy(struct hvutil_transport *hvt)
 	if (hvt->cn_id.idx > 0 && hvt->cn_id.val > 0)
 		cn_del_callback(&hvt->cn_id);
 
-	if (mode_old != HVUTIL_TRANSPORT_CHARDEV)
-		hvt_transport_free(hvt);
+	if (mode_old == HVUTIL_TRANSPORT_CHARDEV)
+		wait_for_completion(&hvt->release);
+
+	hvt_transport_free(hvt);
 }
diff --git a/drivers/hv/hv_utils_transport.h b/drivers/hv/hv_utils_transport.h
index d98f522..79afb62 100644
--- a/drivers/hv/hv_utils_transport.h
+++ b/drivers/hv/hv_utils_transport.h
@@ -41,6 +41,7 @@ struct hvutil_transport {
 	int outmsg_len;                     /* its length */
 	wait_queue_head_t outmsg_q;         /* poll/read wait queue */
 	struct mutex lock;                  /* protects struct members */
+	struct completion release;          /* synchronize with fd release */
 };
 
 struct hvutil_transport *hvutil_transport_init(const char *name,
-- 
2.9.3