[RFC PATCH net-next 07/12] tuntap: simplify error handling in tun_build_skb()

[Jason Wang]

Signed-off-by: Jason Wang <jasow...@redhat.com>
---
 drivers/net/tun.c | 36 ++++++++++++++----------------------
 1 file changed, 14 insertions(+), 22 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 24ecd82..f6e0f96 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1612,7 +1612,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
*tun,
                                     int len, int *skb_xdp)
 {
        struct page_frag *alloc_frag = &current->task_frag;
-       struct sk_buff *skb;
+       struct sk_buff *skb = NULL;
        struct bpf_prog *xdp_prog;
        int buflen = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
        unsigned int delta = 0;
@@ -1638,6 +1638,9 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
*tun,
        if (copied != len)
                return ERR_PTR(-EFAULT);
 
+       get_page(alloc_frag->page);
+       alloc_frag->offset += buflen;
+
        /* There's a small window that XDP may be set after the check
         * of xdp_prog above, this should be rare and for simplicity
         * we do XDP on skb in case the headroom is not enough.
@@ -1665,24 +1668,16 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
*tun,
 
                switch (act) {
                case XDP_REDIRECT:
-                       get_page(alloc_frag->page);
-                       alloc_frag->offset += buflen;
                        err = xdp_do_redirect(tun->dev, &xdp, xdp_prog);
                        xdp_do_flush_map();
                        if (err)
-                               goto err_redirect;
-                       rcu_read_unlock();
-                       preempt_enable();
-                       return NULL;
+                               goto err_xdp;
+                       goto out;
                case XDP_TX:
-                       get_page(alloc_frag->page);
-                       alloc_frag->offset += buflen;
                        if (tun_xdp_tx(tun->dev, &xdp))
-                               goto err_redirect;
+                               goto err_xdp;
                        tun_xdp_flush(tun->dev);
-                       rcu_read_unlock();
-                       preempt_enable();
-                       return NULL;
+                       goto out;
                case XDP_PASS:
                        delta = orig_data - xdp.data;
                        len = xdp.data_end - xdp.data;
@@ -1702,25 +1697,22 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
*tun,
 
        skb = build_skb(buf, buflen);
        if (!skb) {
-               rcu_read_unlock();
-               preempt_enable();
-               return ERR_PTR(-ENOMEM);
+               skb = ERR_PTR(-ENOMEM);
+               goto out;
        }
 
        skb_reserve(skb, pad - delta);
        skb_put(skb, len);
-       get_page(alloc_frag->page);
-       alloc_frag->offset += buflen;
 
        return skb;
 
-err_redirect:
-       put_page(alloc_frag->page);
 err_xdp:
+       alloc_frag->offset -= buflen;
+       put_page(alloc_frag->page);
+out:
        rcu_read_unlock();
        preempt_enable();
-       this_cpu_inc(tun->pcpu_stats->rx_dropped);
-       return NULL;
+       return skb;
 }
 
 /* Get packet from user space buffer */
-- 
2.7.4