[PATCH 10/46] Staging: hv: storvsc: Get rid of the reference counting in struct storvsc_device

["K. Y. Srinivasan" <kys@microsoft.com>]

Get rid of the reference counting in struct storvsc_device. We manage the lifecycle with 
the following logic: If the device is marked for destruction, we dot allow any
outgoing traffic on the device. Incoming traffic is allowed only to drain pending
outgoing traffic. Note that while the upper level code in Linux deals with outstanding
I/Os, we may have situations on Hyper-V where some book keeping messages are sent out
that the upper level Linux code may not be aware of.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
---
 drivers/staging/hv/hyperv_storage.h |   18 ++----------------
 drivers/staging/hv/storvsc.c        |   33 +++++++++++++++++++++------------
 drivers/staging/hv/storvsc_drv.c    |    1 -
 3 files changed, 23 insertions(+), 29 deletions(-)

diff --git a/drivers/staging/hv/hyperv_storage.h b/drivers/staging/hv/hyperv_storage.h
index 1a59ca0..687cdc5 100644
--- a/drivers/staging/hv/hyperv_storage.h
+++ b/drivers/staging/hv/hyperv_storage.h
@@ -264,8 +264,6 @@ struct storvsc_major_info {
 struct storvsc_device {
 	struct hv_device *device;
 
-	/* 0 indicates the device is being destroyed */
-	atomic_t ref_count;
 	bool	 destroy;
 	bool	 drain_notify;
 	atomic_t num_outstanding_req;
@@ -287,32 +285,20 @@ struct storvsc_device {
 };
 
 
-/* Get the stordevice object iff exists and its refcount > 1 */
 static inline struct storvsc_device *get_out_stor_device(
 					struct hv_device *device)
 {
 	struct storvsc_device *stor_device;
 
 	stor_device = (struct storvsc_device *)device->ext;
-	if (stor_device && (atomic_read(&stor_device->ref_count) > 1) &&
-		!stor_device->destroy)
-		atomic_inc(&stor_device->ref_count);
-	else
+
+	if (stor_device && stor_device->destroy)
 		stor_device = NULL;
 
 	return stor_device;
 }
 
 
-static inline void put_stor_device(struct hv_device *device)
-{
-	struct storvsc_device *stor_device;
-
-	stor_device = (struct storvsc_device *)device->ext;
-
-	atomic_dec(&stor_device->ref_count);
-}
-
 static inline void storvsc_wait_to_drain(struct storvsc_device *dev)
 {
 	dev->drain_notify = true;
diff --git a/drivers/staging/hv/storvsc.c b/drivers/staging/hv/storvsc.c
index 3e9829f..fb7b3ca 100644
--- a/drivers/staging/hv/storvsc.c
+++ b/drivers/staging/hv/storvsc.c
@@ -40,9 +40,6 @@ static inline struct storvsc_device *alloc_stor_device(struct hv_device *device)
 	if (!stor_device)
 		return NULL;
 
-	/* Set to 2 to allow both inbound and outbound traffics */
-	/* (ie get_out_stor_device() and get_in_stor_device()) to proceed. */
-	atomic_set(&stor_device->ref_count, 2);
 	stor_device->destroy = false;
 	init_waitqueue_head(&stor_device->waiting_to_drain);
 	stor_device->device = device;
@@ -52,19 +49,31 @@ static inline struct storvsc_device *alloc_stor_device(struct hv_device *device)
 }
 
 
-/* Get the stordevice object iff exists and its refcount > 0 */
 static inline struct storvsc_device *get_in_stor_device(
 					struct hv_device *device)
 {
 	struct storvsc_device *stor_device;
+	unsigned long flags;
 
+	spin_lock_irqsave(&device->channel->inbound_lock, flags);
 	stor_device = (struct storvsc_device *)device->ext;
-	if (stor_device && atomic_read(&stor_device->ref_count))
-		atomic_inc(&stor_device->ref_count);
-	else
+
+	if (!stor_device)
+		goto get_in_err;
+
+	/*
+	 * If the device is being destroyed; allow incoming
+	 * traffic only to cleanup outstanding requests.
+	 */
+
+	if (stor_device->destroy  &&
+		(atomic_read(&stor_device->num_outstanding_req) == 0))
 		stor_device = NULL;
 
+get_in_err:
+	spin_unlock_irqrestore(&device->channel->inbound_lock, flags);
 	return stor_device;
+
 }
 
 static int storvsc_channel_init(struct hv_device *device)
@@ -190,7 +199,6 @@ static int storvsc_channel_init(struct hv_device *device)
 
 
 cleanup:
-	put_stor_device(device);
 	return ret;
 }
 
@@ -303,7 +311,6 @@ static void storvsc_on_channel_callback(void *context)
 		}
 	} while (1);
 
-	put_stor_device(device);
 	return;
 }
 
@@ -371,7 +378,6 @@ int storvsc_dev_remove(struct hv_device *device)
 	unsigned long flags;
 
 	stor_device = (struct storvsc_device *)device->ext;
-	atomic_dec(&stor_device->ref_count);
 
 	spin_lock_irqsave(&device->channel->inbound_lock, flags);
 	stor_device->destroy = true;
@@ -388,9 +394,13 @@ int storvsc_dev_remove(struct hv_device *device)
 	/*
 	 * Since we have already drained, we don't need to busy wait
 	 * as was done in final_release_stor_device()
+	 * Note that we cannot set the ext pointer to NULL until
+	 * we have drained - to drain the outgoing packets, we need to
+	 * allow incoming packets.
 	 */
-	atomic_set(&stor_device->ref_count, 0);
+	spin_lock_irqsave(&device->channel->inbound_lock, flags);
 	device->ext = NULL;
+	spin_unlock_irqrestore(&device->channel->inbound_lock, flags);
 
 	/* Close the channel */
 	vmbus_close(device->channel);
@@ -448,7 +458,6 @@ int storvsc_do_io(struct hv_device *device,
 
 	atomic_inc(&stor_device->num_outstanding_req);
 
-	put_stor_device(device);
 	return ret;
 }
 
diff --git a/drivers/staging/hv/storvsc_drv.c b/drivers/staging/hv/storvsc_drv.c
index 5b2004f..ae74f50 100644
--- a/drivers/staging/hv/storvsc_drv.c
+++ b/drivers/staging/hv/storvsc_drv.c
@@ -378,7 +378,6 @@ static int storvsc_host_reset(struct hv_device *device)
 	 */
 
 cleanup:
-	put_stor_device(device);
 	return ret;
 }
 
-- 
1.7.4.1