netdev - Re: [PATCH v2] xen-netfront: Fix Rx stall during network stress and OOM

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Message-ID: <989bd104-13a9-f25f-b857-24ec49781f9c@amazon.com>
Date:   Mon, 30 Jan 2017 08:47:52 -0800
From:   Vineeth Remanan Pillai <vineethp@...zon.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        <linux-kernel@...r.kernel.org>
CC:     David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
        Wei Liu <wei.liu2@...rix.com>,
        Paul Durrant <paul.durrant@...rix.com>,
        xen-devel <xen-devel@...ts.xen.org>
Subject: Re: [PATCH v2] xen-netfront: Fix Rx stall during network stress and
 OOM


On 01/29/2017 03:09 PM, Boris Ostrovsky wrote:
>
> There are couple of problems with this patch.
> 1. The 'if' clause now evaluates to true on pretty much every call to 
> xennet_alloc_rx_buffers().
Thanks for catching this. In my testing I did not notice this - mostly 
because of the nature of the workload in my testing.

> 2. It tickles a latent bug during resume where the timer triggers 
> before we re-connect. The trouble is that we now try to dereference 
> queue->rx.sring which is NULL since we disconnect in 
> netfront_resume(). (Curiously, I only observe it with 32-bit guests)
I think we may hit this bug after removing the timer as well. We call 
RING_PUSH_REQUESTS_AND_CHECK_NOTIFY soon after, which also dereference 
queue->rx.sring.

Thanks,
Vineeth