hv_netvsc: Restore needed_headroom request
authorVitaly Kuznetsov <vkuznets@redhat.com>
Fri, 5 Feb 2016 16:29:08 +0000 (17:29 +0100)
committerDavid S. Miller <davem@davemloft.net>
Sat, 13 Feb 2016 11:04:44 +0000 (06:04 -0500)
commit14a03cf80edf3e19953bb744938e48bc9d496d30
treefbf90e3b99b0108ff53fc076faa7418a4391d5e7
parent603607de0c574e693e7cfda1aba64bf4439875b7
hv_netvsc: Restore needed_headroom request

Commit c0eb454034aa ("hv_netvsc: Don't ask for additional head room in the
skb") got rid of needed_headroom setting for the driver. With the change I
hit the following issue trying to use ptkgen module:

[   57.522021] kernel BUG at net/core/skbuff.c:1128!
[   57.522021] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
...
[   58.721068] Call Trace:
[   58.721068]  [<ffffffffa0144e86>] netvsc_start_xmit+0x4c6/0x8e0 [hv_netvsc]
...
[   58.721068]  [<ffffffffa02f87fc>] ? pktgen_finalize_skb+0x25c/0x2a0 [pktgen]
[   58.721068]  [<ffffffff814f5760>] ? __netdev_alloc_skb+0xc0/0x100
[   58.721068]  [<ffffffffa02f9907>] pktgen_thread_worker+0x257/0x1920 [pktgen]

Basically, we're calling skb_cow_head(skb, RNDIS_AND_PPI_SIZE) and crash on
    if (skb_shared(skb))
        BUG();

We probably need to restore needed_headroom setting (but shrunk to
RNDIS_AND_PPI_SIZE as we don't need more) to request the required headroom
space. In theory, it should not give us performance penalty.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
drivers/net/hyperv/netvsc_drv.c