netdev - RE: [Patch v9 03/12] net: mana: Handle vport sharing between devices

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Date:   Tue, 25 Oct 2022 01:43:16 +0000
From:   Long Li <longli@...rosoft.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "shiraz.saleem@...el.com" <shiraz.saleem@...el.com>,
        Ajay Sharma <sharmaajay@...rosoft.com>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: RE: [Patch v9 03/12] net: mana: Handle vport sharing between devices

> >>> @@ -679,9 +714,16 @@ static int mana_cfg_vport(struct
> >>> mana_port_context *apc, u32 protection_dom_id,
> >>>
> >>>  	apc->tx_shortform_allowed = resp.short_form_allowed;
> >>>  	apc->tx_vp_offset = resp.tx_vport_offset;
> >>> +
> >>> +	netdev_info(apc->ndev, "Configured vPort %llu PD %u DB %u\n",
> >>> +		    apc->port_handle, protection_dom_id, doorbell_pg_id);
> >>>  out:
> >>> +	if (err)
> >>> +		mana_uncfg_vport(apc);
> >>
> >> There seems to be a similar race between error handling here and the
> >> "apc-
> >>> vport_use_count > 0" checking above as pointed out in v7.
> >
> > Thanks for looking into this.
> >
> > This is different to the locking bug in mana_ib_cfg_vport(). The vport
> > sharing between Ethernet and RDMA is exclusive, not shared. If another
> > driver tries to take the vport while it is being configured, it will
> > fail immediately. It is by
> 
> Suppose the following steps:
> 1. Ethernet driver take the lock first and do a "apc->vport_use_count++",
> and
>    release the lock;
> 2. RDMA driver take the lock, do "apc->vport_use_count > 0" checking and
> return
>    -EBUSY;
> 3. mana_send_request() or mana_verify_resp_hdr() return error to
> Ethernet driver.
> 
> It seems that vport is left unused when above happens, if that is what you
> wanted?

Yes, in this case the vport is left unused. There is no resource leak.
This is expected.

> 
> 
> > design to prevent possible deadlock.
> 
> I am not sure I understand the deadlock here.

Because we are dealing with two drivers. I don't want to block as
mana_send_request() is a blocking call.