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SubjectRe: [PATCH] tun: make tun_build_skb() thread safe
On Wed, Aug 16, 2017 at 10:14:33PM +0800, Jason Wang wrote:
> From: Eric Dumazet <eric.dumazet@gmail.com>
>
> tun_build_skb() is not thread safe since it uses per queue page frag,
> this will break things when multiple threads are sending through same
> queue. Switch to use per-thread generator (no lock involved).
>
> Fixes: 66ccbc9c87c2 ("tap: use build_skb() for small packet")
> Tested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

Jason, given the switch to task_frag, would it be worth it to look at
using higher order allocs along the lines of
5640f7685831e088fe6c2e1f863a6805962f8e81 as well?

> ---
> drivers/net/tun.c | 7 +------
> 1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 5892284..c38cd84 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -175,7 +175,6 @@ struct tun_file {
> struct list_head next;
> struct tun_struct *detached;
> struct skb_array tx_array;
> - struct page_frag alloc_frag;
> };
>
> struct tun_flow_entry {
> @@ -578,8 +577,6 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
> }
> if (tun)
> skb_array_cleanup(&tfile->tx_array);
> - if (tfile->alloc_frag.page)
> - put_page(tfile->alloc_frag.page);
> sock_put(&tfile->sk);
> }
> }
> @@ -1272,7 +1269,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
> struct virtio_net_hdr *hdr,
> int len, int *generic_xdp)
> {
> - struct page_frag *alloc_frag = &tfile->alloc_frag;
> + struct page_frag *alloc_frag = &current->task_frag;
> struct sk_buff *skb;
> struct bpf_prog *xdp_prog;
> int buflen = SKB_DATA_ALIGN(len + TUN_RX_PAD) +
> @@ -2580,8 +2577,6 @@ static int tun_chr_open(struct inode *inode, struct file * file)
> tfile->sk.sk_write_space = tun_sock_write_space;
> tfile->sk.sk_sndbuf = INT_MAX;
>
> - tfile->alloc_frag.page = NULL;
> -
> file->private_data = tfile;
> INIT_LIST_HEAD(&tfile->next);
>
> --
> 2.7.4

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