Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx> writes:
> With new transparent VF support, it is possible to get a deadlock
> when some of the deferred work is running and the unregister_vf
> is trying to cancel the work element. The solution is to use
> trylock and reschedule (similar to bonding and team device).
>
> Reported-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> Fixes: 0c195567a8f6 ("netvsc: transparent VF management")
> Signed-off-by: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
> ---
> drivers/net/hyperv/netvsc_drv.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index c71728d82049..e75c0f852a63 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -1601,7 +1601,11 @@ static void netvsc_vf_setup(struct work_struct *w)
> struct net_device *ndev = hv_get_drvdata(ndev_ctx->device_ctx);
> struct net_device *vf_netdev;
>
> - rtnl_lock();
> + if (!rtnl_trylock()) {
> + schedule_work(w);
> + return;
> + }
> +
> vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
> if (vf_netdev)
> __netvsc_vf_setup(ndev, vf_netdev);
> @@ -1655,7 +1659,11 @@ static void netvsc_vf_update(struct work_struct *w)
> struct net_device *vf_netdev;
> bool vf_is_up;
>
> - rtnl_lock();
> + if (!rtnl_trylock()) {
> + schedule_work(w);
> + return;
> + }
> +
So in the situation when we're currently in netvsc_unregister_vf() and
trying to do
cancel_work_sync(&net_device_ctx->vf_takeover);
cancel_work_sync(&net_device_ctx->vf_notify);
we'll end up not executing netvsc_vf_update() at all, right? Wouldn't it
create an issue as nobody is switching the datapath back to netvsc?
> vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
> if (!vf_netdev)
> goto unlock;
--
Vitaly
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