netdev - Re: [PATCH net] ibmvnic: Clean RX pools only during a hard reset

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Message-Id: <6bc62728-e3b0-a9ef-242b-abf3e9d1cc90@linux.vnet.ibm.com>
Date:   Mon, 19 Feb 2018 14:01:00 -0600
From:   Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, nfont@...ux.vnet.ibm.com,
        jallen@...ux.vnet.ibm.com
Subject: Re: [PATCH net] ibmvnic: Clean RX pools only during a hard reset

On 02/19/2018 01:30 PM, David Miller wrote:
> From: Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>
> Date: Mon, 19 Feb 2018 13:24:52 -0600
>
>> Sorry, I should explain it better. It's not there is a double free.
>> It's that the driver is receiving RX descriptors from the previous
>> session for which socket buffers have been freed. The driver's
>> polling routine tries to copy data to the socket buffer, but it's
>> been freed, so it's trying to copy to a NULL pointer.
> That's kinda hairy, is this resend of the old descriptors guaranteed
> to always happen in this situation?
>
> Maybe it's better to have some way for the RX descriptor receiving
> path to detect this situation (is SKB slot NULL?) to handle the
> problem there.

It is something we can expect to happen in this situation.  Thanks for the suggestion.  That way the driver can free up that memory when it closes.  I'll try to get a v2 out soon.

Thanks again.

> Thanks.
>