On Sun, 2015-11-01 at 15:58 -0500, David Miller wrote:

From: Eric Dumazet <redacted>
Date: Sun, 01 Nov 2015 09:20:59 -0800

quoted

From: Eric Dumazet <edumazet@google.com>

My recent commit, attaching SYNACK messages to request sockets
exposed a too small LL_MAX_HEADER when netvsc_drv.c is in use,
because this driver sets a needed_headroom of 220 bytes.

Increase LL_MAX_HEADER in this case, to avoid a realloc of all
TCP frames.

In another patch, I'll make skb_set_owner_w() more robust.

Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Bisected-by: Haiyang Zhang [off-list ref]

Using a value of 256 just because HYPER-V is crazy imposes a huge
unnecessary burdon upon the rest of the stack.

I rejected a previous attempt to use such a huge value for
LL_MAX_HEADER, and I will do so again here.  We need a different fix
for this issue, one that doesn't hurt everyone.

Sure, I was planning to send the skb_set_owner_w() fix as well.

I was not aware you already objected to LL_MAX_HEADER increase.