netdev - RE: [PATCH net-next 1/1] hv_netvsc: fix deadlock on hotplug

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Message-ID: <DM5PR21MB0475451095CC657BB54C4E50CA970@DM5PR21MB0475.namprd21.prod.outlook.com>
Date:   Wed, 6 Sep 2017 16:23:45 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>
CC:     "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next 1/1] hv_netvsc: fix deadlock on hotplug



> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@...workplumber.org]
> Sent: Wednesday, September 6, 2017 11:19 AM
> To: KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang
> <haiyangz@...rosoft.com>; Stephen Hemminger <sthemmin@...rosoft.com>
> Cc: devel@...uxdriverproject.org; netdev@...r.kernel.org
> Subject: [PATCH net-next 1/1] hv_netvsc: fix deadlock on hotplug
> 
> When a virtual device is added dynamically (via host console), then
> the vmbus sends an offer message for the primary channel. The processing
> of this message for networking causes the network device to then
> initialize the sub channels.
> 
> The problem is that setting up the sub channels needs to wait until
> the subsequent subchannel offers have been processed. These offers
> come in on the same ring buffer and work queue as where the primary
> offer is being processed; leading to a deadlock.
> 
> This did not happen in older kernels, because the sub channel waiting
> logic was broken (it wasn't really waiting).
> 
> The solution is to do the sub channel setup in its own work queue
> context that is scheduled by the primary channel setup; and then
> happens later.
> 
> Fixes: 732e49850c5e ("netvsc: fix race on sub channel creation")
> Reported-by: Dexuan Cui <decui@...rosoft.com>
> Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>
> ---
> Should also go to stable, but this version does not apply cleanly
> to 4.13. Have another patch for that.
> 
>  drivers/net/hyperv/hyperv_net.h   |   1 +
>  drivers/net/hyperv/netvsc_drv.c   |   8 +--
>  drivers/net/hyperv/rndis_filter.c | 106 ++++++++++++++++++++++++++-----
> -------
>  3 files changed, 74 insertions(+), 41 deletions(-)

The patch looks overall. I just have a question:

With this patch, after module load and probe is done, there may still be
subchannels being processed. If rmmod immediately, the subchannel offers 
may hit half-way removed device structures... Do we also need to add 
cancel_work_sync(&dev->subchan_work) to the top of netvsc_remove()?

unregister_netdevice() includes device close, but it's only called later
in the netvsc_remove() when rndis is already removed.

Thanks,
- Haiyang