Re: [PATCH net] hv_netvsc: Restore needed_headroom request

From	David Miller <davem@davemloft.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH net] hv_netvsc: Restore needed_headroom request
Date	2016-02-13 12:10 +0100
Message-ID	<r1Gfo-3Vl-19@gated-at.bofh.it> (permalink)
References	<qYRqG-2CN-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Fri,  5 Feb 2016 17:29:08 +0100

> 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>

Applied, thanks.

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Re: [PATCH net] hv_netvsc: Restore needed_headroom request David Miller <davem@davemloft.net> - 2016-02-13 12:10 +0100

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