On 2020/12/3 下午4:00, wangyunjian wrote:
From: Yunjian Wang <wangyunjian@xxxxxxxxxx>
After setting callback for ubuf_info of skb, the callback
(vhost_net_zerocopy_callback) will be called to decrease
the refcount when freeing skb. But when an exception occurs
afterwards, the error handling in vhost handle_tx() will
try to decrease the same refcount again. This is wrong and
fix this by clearing ubuf_info when meeting errors.
Fixes: 4477138fa0ae ("tun: properly test for IFF_UP")
Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
Signed-off-by: Yunjian Wang <wangyunjian@xxxxxxxxxx>
---
drivers/net/tun.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2dc1988a8973..3614bb1b6d35 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1861,6 +1861,12 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
if (unlikely(!(tun->dev->flags & IFF_UP))) {
err = -EIO;
rcu_read_unlock();
+ if (zerocopy) {
+ skb_shinfo(skb)->destructor_arg = NULL;
+ skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;
+ skb_shinfo(skb)->tx_flags &= ~SKBTX_SHARED_FRAG;
+ }
+
goto drop;
}
@@ -1874,6 +1880,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
if (unlikely(headlen > skb_headlen(skb))) {
atomic_long_inc(&tun->dev->rx_dropped);
+ if (zerocopy) {
+ skb_shinfo(skb)->destructor_arg = NULL;
+ skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;
+ skb_shinfo(skb)->tx_flags &= ~SKBTX_SHARED_FRAG;
+ }
napi_free_frags(&tfile->napi);
rcu_read_unlock();
mutex_unlock(&tfile->napi_mutex);
It looks to me then we miss the failure feedback.
The issues comes from the inconsistent error handling in tun.
I wonder whether we can simply do uarg->callback(uarg, false) if
necessary on every failture path on tun_get_user().
Note that, zerocopy has a lot of issues which makes it not good for
production environment.
Thanks
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