[PATCH 115/117] Staging: hv: vmbus: Properly deal with de-registering channel callback

[K. Y. Srinivasan]

Ensure that we correctly handle racing invocations of the channel callback
when the channel is being closed. We do this using the channel's inbound_lock.
A side-effect of this strategy is that we avoid repeatedly picking up this lock
as we drain the inbound ring-buffer.

Signed-off-by: K. Y. Srinivasan <kys at microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz at microsoft.com>
---
 drivers/staging/hv/channel.c    |   20 +++++---------------
 drivers/staging/hv/connection.c |    3 +++
 2 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/staging/hv/channel.c b/drivers/staging/hv/channel.c
index ac92c1f..b6f3d38 100644
--- a/drivers/staging/hv/channel.c
+++ b/drivers/staging/hv/channel.c
@@ -513,9 +513,12 @@ void vmbus_close(struct vmbus_channel *channel)
 {
 	struct vmbus_channel_close_channel *msg;
 	int ret;
+	unsigned long flags;
 
 	/* Stop callback and cancel the timer asap */
+	spin_lock_irqsave(&channel->inbound_lock, flags);
 	channel->onchannel_callback = NULL;
+	spin_unlock_irqrestore(&channel->inbound_lock, flags);
 
 	/* Send a closing message */
 
@@ -735,19 +738,15 @@ int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
 	u32 packetlen;
 	u32 userlen;
 	int ret;
-	unsigned long flags;
 
 	*buffer_actual_len = 0;
 	*requestid = 0;
 
-	spin_lock_irqsave(&channel->inbound_lock, flags);
 
 	ret = hv_ringbuffer_peek(&channel->inbound, &desc,
 			     sizeof(struct vmpacket_descriptor));
-	if (ret != 0) {
-		spin_unlock_irqrestore(&channel->inbound_lock, flags);
+	if (ret != 0)
 		return 0;
-	}
 
 	packetlen = desc.len8 << 3;
 	userlen = packetlen - (desc.offset8 << 3);
@@ -755,7 +754,6 @@ int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
 	*buffer_actual_len = userlen;
 
 	if (userlen > bufferlen) {
-		spin_unlock_irqrestore(&channel->inbound_lock, flags);
 
 		pr_err("Buffer too small - got %d needs %d\n",
 			   bufferlen, userlen);
@@ -768,7 +766,6 @@ int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
 	ret = hv_ringbuffer_read(&channel->inbound, buffer, userlen,
 			     (desc.offset8 << 3));
 
-	spin_unlock_irqrestore(&channel->inbound_lock, flags);
 
 	return 0;
 }
@@ -785,19 +782,15 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
 	u32 packetlen;
 	u32 userlen;
 	int ret;
-	unsigned long flags;
 
 	*buffer_actual_len = 0;
 	*requestid = 0;
 
-	spin_lock_irqsave(&channel->inbound_lock, flags);
 
 	ret = hv_ringbuffer_peek(&channel->inbound, &desc,
 			     sizeof(struct vmpacket_descriptor));
-	if (ret != 0) {
-		spin_unlock_irqrestore(&channel->inbound_lock, flags);
+	if (ret != 0)
 		return 0;
-	}
 
 
 	packetlen = desc.len8 << 3;
@@ -806,8 +799,6 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
 	*buffer_actual_len = packetlen;
 
 	if (packetlen > bufferlen) {
-		spin_unlock_irqrestore(&channel->inbound_lock, flags);
-
 		pr_err("Buffer too small - needed %d bytes but "
 			"got space for only %d bytes\n",
 			packetlen, bufferlen);
@@ -819,7 +810,6 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
 	/* Copy over the entire packet to the user buffer */
 	ret = hv_ringbuffer_read(&channel->inbound, buffer, packetlen, 0);
 
-	spin_unlock_irqrestore(&channel->inbound_lock, flags);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(vmbus_recvpacket_raw);
diff --git a/drivers/staging/hv/connection.c b/drivers/staging/hv/connection.c
index 7a3ec75..6aab802 100644
--- a/drivers/staging/hv/connection.c
+++ b/drivers/staging/hv/connection.c
@@ -215,6 +215,7 @@ struct vmbus_channel *relid2channel(u32 relid)
 static void process_chn_event(u32 relid)
 {
 	struct vmbus_channel *channel;
+	unsigned long flags;
 
 	/*
 	 * Find the channel based on this relid and invokes the
@@ -222,11 +223,13 @@ static void process_chn_event(u32 relid)
 	 */
 	channel = relid2channel(relid);
 
+	spin_lock_irqsave(&channel->inbound_lock, flags);
 	if (channel && (channel->onchannel_callback != NULL)) {
 		channel->onchannel_callback(channel->channel_callback_context);
 	} else {
 		pr_err("channel not found for relid - %u\n", relid);
 	}
+	spin_unlock_irqrestore(&channel->inbound_lock, flags);
 }
 
 /*
-- 
1.7.4.1