netdev - Re: [PATCH v2] xen-netfront: fix potential deadlock in xennet

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Message-Id: <20200724.170220.1275270219725381485.davem@davemloft.net>
Date:   Fri, 24 Jul 2020 17:02:20 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     andrea.righi@...onical.com
Cc:     boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org, kuba@...nel.org,
        xen-devel@...ts.xenproject.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] xen-netfront: fix potential deadlock in
 xennet_remove()

From: Andrea Righi <andrea.righi@...onical.com>
Date: Fri, 24 Jul 2020 10:59:10 +0200

> There's a potential race in xennet_remove(); this is what the driver is
> doing upon unregistering a network device:
> 
>   1. state = read bus state
>   2. if state is not "Closed":
>   3.    request to set state to "Closing"
>   4.    wait for state to be set to "Closing"
>   5.    request to set state to "Closed"
>   6.    wait for state to be set to "Closed"
> 
> If the state changes to "Closed" immediately after step 1 we are stuck
> forever in step 4, because the state will never go back from "Closed" to
> "Closing".
> 
> Make sure to check also for state == "Closed" in step 4 to prevent the
> deadlock.
> 
> Also add a 5 sec timeout any time we wait for the bus state to change,
> to avoid getting stuck forever in wait_event().
> 
> Signed-off-by: Andrea Righi <andrea.righi@...onical.com>
> ---
> Changes in v2:
>  - remove all dev_dbg() calls (as suggested by David Miller)

Applied, thank you.