netdev - Re: [PATCH] hv_netvsc: fix send buffer failure on MTU change

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Message-Id: <20170921.151841.2164510833838294238.davem@davemloft.net>
Date:   Thu, 21 Sep 2017 15:18:41 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     stephen@...workplumber.org
Cc:     kys@...rosoft.com, netdev@...r.kernel.org, alexng@...rosoft.com,
        sthemmin@...rosoft.com
Subject: Re: [PATCH] hv_netvsc: fix send buffer failure on MTU change

From: Stephen Hemminger <stephen@...workplumber.org>
Date: Wed, 20 Sep 2017 11:17:35 -0700

> From: Alex Ng <alexng@...rosoft.com>
> 
> If MTU is changed the host would reject the send buffer change.
> This problem is result of recent change to allow changing send
> buffer size.
> 
> Every time we change the MTU, we store the previous net_device section
> count before destroying the buffer, but we don’t store the previous
> section size. When we reinitialize the buffer, its size is calculated
> by multiplying the previous count and previous size. Since we
> continuously increase the MTU, the host returns us a decreasing count
> value while the section size is reinitialized to 1728 bytes every
> time.
> 
> This eventually leads to a condition where the calculated buf_size is
> so small that the host rejects it.
> 
> Fixes: 8b5327975ae1 ("netvsc: allow controlling send/recv buffer size")
> Signed-off-by: Alex Ng <alexng@...rosoft.com>
> Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>

Applied, thank you.