Drivers: hv: vmbus: Fix rescind handling issues

commit 6f3d791f300618caf82a2be0c27456edd76d5164 upstream.

This patch handles the following issues that were observed when we are
handling racing channel offer message and rescind message for the same
offer:

1. Since the host does not respond to messages on a rescinded channel,
in the current code, we could be indefinitely blocked on the vmbus_open() call.

2. When a rescinded channel is being closed, if there is a pending interrupt on the
channel, we could end up freeing the channel that the interrupt handler would run on.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Tested-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 45 insertions, 3 deletions

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index e57cc40cb768..63ac1c6a825f 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -177,6 +177,11 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
 		      &vmbus_connection.chn_msg_list);
 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
 
+	if (newchannel->rescind) {
+		err = -ENODEV;
+		goto error_free_gpadl;
+	}
+
 	ret = vmbus_post_msg(open_msg,
 			     sizeof(struct vmbus_channel_open_channel), true);
 
@@ -421,6 +426,11 @@ int vmbus_establish_gpadl(struct vmbus_channel *channel, void *kbuffer,
 
 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
 
+	if (channel->rescind) {
+		ret = -ENODEV;
+		goto cleanup;
+	}
+
 	ret = vmbus_post_msg(gpadlmsg, msginfo->msgsize -
 			     sizeof(*msginfo), true);
 	if (ret != 0)
@@ -494,6 +504,10 @@ int vmbus_teardown_gpadl(struct vmbus_channel *channel, u32 gpadl_handle)
 	list_add_tail(&info->msglistentry,
 		      &vmbus_connection.chn_msg_list);
 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+
+	if (channel->rescind)
+		goto post_msg_err;
+
 	ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_gpadl_teardown),
 			     true);
 
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 037361158074..624d815745e4 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -451,6 +451,12 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 	/* Make sure this is a new offer */
 	mutex_lock(&vmbus_connection.channel_mutex);
 
+	/*
+	 * Now that we have acquired the channel_mutex,
+	 * we can release the potentially racing rescind thread.
+	 */
+	atomic_dec(&vmbus_connection.offer_in_progress);
+
 	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
 		if (!uuid_le_cmp(channel->offermsg.offer.if_type,
 			newchannel->offermsg.offer.if_type) &&
@@ -481,7 +487,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 			channel->num_sc++;
 			spin_unlock_irqrestore(&channel->lock, flags);
 		} else {
-			atomic_dec(&vmbus_connection.offer_in_progress);
 			goto err_free_chan;
 		}
 	}
@@ -510,7 +515,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 	if (!fnew) {
 		if (channel->sc_creation_callback != NULL)
 			channel->sc_creation_callback(newchannel);
-		atomic_dec(&vmbus_connection.offer_in_progress);
 		return;
 	}
 
@@ -541,7 +545,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 		goto err_deq_chan;
 	}
 
-	atomic_dec(&vmbus_connection.offer_in_progress);
+	newchannel->probe_done = true;
 	return;
 
 err_deq_chan:
@@ -882,8 +886,27 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
 	channel->rescind = true;
 	spin_unlock_irqrestore(&channel->lock, flags);
 
+	/*
+	 * Now that we have posted the rescind state, perform
+	 * rescind related cleanup.
+	 */
 	vmbus_rescind_cleanup(channel);
 
+	/*
+	 * Now wait for offer handling to complete.
+	 */
+	while (READ_ONCE(channel->probe_done) == false) {
+		/*
+		 * We wait here until any channel offer is currently
+		 * being processed.
+		 */
+		msleep(1);
+	}
+
+	/*
+	 * At this point, the rescind handling can proceed safely.
+	 */
+
 	if (channel->device_obj) {
 		if (channel->chn_rescind_callback) {
 			channel->chn_rescind_callback(channel);
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index ed84e96715a0..43160a2eafe0 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -940,6 +940,9 @@ static void vmbus_chan_sched(struct hv_per_cpu_context *hv_cpu)
 			if (channel->offermsg.child_relid != relid)
 				continue;
 
+			if (channel->rescind)
+				continue;
+
 			switch (channel->callback_mode) {
 			case HV_CALL_ISR:
 				vmbus_channel_isr(channel);
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index b7d7bbec74e0..fa9fea5765a7 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -895,6 +895,8 @@ struct vmbus_channel {
 	 */
 	enum hv_numa_policy affinity_policy;
 
+	bool probe_done;
+
 };
 
 static inline bool is_hvsock_channel(const struct vmbus_channel *c)