From: "Michael S. Tsirkin" <mst@redhat•com>
To: Jason Wang <jasowang@redhat•com>
Cc: davem@davemloft•net, netdev@vger•kernel.org,
linux-kernel@vger•kernel.org
Subject: Re: [PATCH net 1/2] tuntap: correctly linearize skb when zerocopy is used
Date: Tue, 9 Jul 2013 13:34:52 +0300 [thread overview]
Message-ID: <20130709103452.GB14321@redhat.com> (raw)
In-Reply-To: <1373364651-10474-1-git-send-email-jasowang@redhat.com>
On Tue, Jul 09, 2013 at 06:10:50PM +0800, Jason Wang wrote:
> Userspace may produce vectors greater than MAX_SKB_FRAGS. When we try to
> linearize parts of the skb to let the rest of iov to be fit in
> the frags, we need count copylen into linear when calling tun_alloc_skb()
> instead of partly counting it into data_len. Since this breaks
> zerocopy_sg_from_iovec() since its inner counter assumes nr_frags should
> be zero at beginning. This cause nr_frags to be increased wrongly without
> setting the correct frags.
>
> This bug were introduced from 0690899b4d4501b3505be069b9a687e68ccbe15b
> (tun: experimental zero copy tx support)
>
> Cc: Michael S. Tsirkin <mst@redhat•com>
> Signed-off-by: Jason Wang <jasowang@redhat•com>
> ---
> This patch is needed for stable.
> ---
> drivers/net/tun.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 7eab5fc..01d5a86 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1109,7 +1109,8 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> } else
> copylen = len;
>
> - skb = tun_alloc_skb(tfile, align, copylen, gso.hdr_len, noblock);
> + skb = tun_alloc_skb(tfile, align, copylen,
> + zerocopy ? copylen : gso.hdr_len, noblock);
> if (IS_ERR(skb)) {
> if (PTR_ERR(skb) != -EAGAIN)
> tun->dev->stats.rx_dropped++;
Good catch, thanks. But let's add a new variable and
set it in the if statement above
instead of an extra branch here - not for performance but
because it's clearer this way.
> --
> 1.7.1
prev parent reply other threads:[~2013-07-09 10:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-09 10:10 [PATCH net 1/2] tuntap: correctly linearize skb when zerocopy is used Jason Wang
2013-07-09 10:10 ` [PATCH net 2/2] macvtap: " Jason Wang
2013-07-09 10:35 ` Michael S. Tsirkin
2013-07-10 5:17 ` Jason Wang
2013-07-09 10:34 ` Michael S. Tsirkin [this message]
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