[x/azure][PATCH 17/17] vmbus: fix subchannel removal

[Marcelo Henrique Cerri]

From: Dexuan Cui <decui at microsoft.com>

BugLink: http://bugs.launchpad.net/bugs/1812123

The changes to split ring allocation from open/close, broke
the cleanup of subchannels. This resulted in problems using
uio on network devices because the subchannel was left behind
when the network device was unbound.

The cause was in the disconnect logic which used list splice
to move the subchannel list into a local variable. This won't
work because the subchannel list is needed later during the
process of the rescind messages (relid2channel).

The fix is to just leave the subchannel list in place
which is what the original code did. The list is cleaned
up later when the host rescind is processed.

Without the fix, we have a lot of "hang" issues in netvsc when we
try to change the NIC's MTU, set the number of channels, etc.

Fixes: ae6935ed7d42 ("vmbus: split ring buffer allocation from open")
Cc: stable at vger.kernel.org
Signed-off-by: Stephen Hemminger <sthemmin at microsoft.com>
Signed-off-by: Dexuan Cui <decui at microsoft.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
(backported from commit b5679cebf780c6f1c2451a73bf1842a4409840e7)
[marcelo.cerri: kept `channel->num_sc = 0;` to avoid cherry picking
 4d3c5c69191f ("Drivers: hv: vmbus: Remove the useless API
 vmbus_get_outgoing_channel()")]
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 drivers/hv/channel.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 1bbf048dd931..cfea80530325 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -696,20 +696,14 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
 int vmbus_disconnect_ring(struct vmbus_channel *channel)
 {
 	struct vmbus_channel *cur_channel, *tmp;
-	unsigned long flags;
-	LIST_HEAD(list);
 	int ret;
 
 	if (channel->primary_channel != NULL)
 		return -EINVAL;
 
-	/* Snapshot the list of subchannels */
-	spin_lock_irqsave(&channel->lock, flags);
-	list_splice_init(&channel->sc_list, &list);
 	channel->num_sc = 0;
-	spin_unlock_irqrestore(&channel->lock, flags);
 
-	list_for_each_entry_safe(cur_channel, tmp, &list, sc_list) {
+	list_for_each_entry_safe(cur_channel, tmp, &channel->sc_list, sc_list) {
 		if (cur_channel->rescind)
 			wait_for_completion(&cur_channel->rescind_event);
 
-- 
2.20.1