Re: [dpdk-dev] Problems running netvsc multiq

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 07 Dec 2018 13:15:43 +0200
Mohammed Gamal <mgamal@redhat.com> wrote:

> On Wed, 2018-12-05 at 14:32 -0800, Stephen Hemminger wrote:
> > The problem is a regression in 4.20 kernel. Bisecting now.  
> 
> I was bisecting the kernel and the change that seems to introduce this
> regression is this one:
> 
> commit ae6935ed7d424ffa74d634da00767e7b03c98fd3
> Author: Stephen Hemminger <stephen@networkplumber.org>
> Date:   Fri Sep 14 09:10:17 2018 -0700
> 
>     vmbus: split ring buffer allocation from open
>     
>     The UIO driver needs the ring buffer to be persistent(reused)
>     across open/close. Split the allocation and setup of ring buffer
>     out of vmbus_open. For normal usage vmbus_open/vmbus_close there
>     are no changes; only impacts uio_hv_generic which needs to keep
>     ring buffer memory and reuse when application restarts.
>     
>     Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
>     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 

Patch posted: 

From stephen@networkplumber.org Fri Dec  7 10:58:47 2018
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: [PATCH] vmbus: fix subchannel removal

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.

Fixes: ae6935ed7d42 ("vmbus: split ring buffer allocation from open")
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
---
 drivers/hv/channel.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index fe00b12e4417..bea4c9850247 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -701,20 +701,12 @@ 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);
 
-- 
2.19.2