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SubjectRe: [PATCH net-next V2 1/3] tap: use build_skb() for small packet
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On Wed, 2017-08-16 at 11:55 +0800, Jason Wang wrote:
>
> On 2017年08月16日 11:45, Eric Dumazet wrote:
> >
> > You do realize that tun_build_skb() is not thread safe ?
>
> Ok, I think the issue if skb_page_frag_refill(), need a spinlock
> probably. Will prepare a patch.

But since tun is used from process context, why don't you use the
per-thread generator (no lock involved)

tcp_sendmsg() uses this for GFP_KERNEL allocations.

Untested patch :

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 5892284eb8d05b0678d820bad3d0d2c61a879aeb..c38cd840cc0b7fecf182b23976e36f709cacca1f 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);




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