The TAP can be used as vhost-net backend. E.g., the tap_handle_frame() is
the interface to forward the skb from TAP to vhost-net/virtio-net.
However, there are many "goto drop" in the TAP driver. Therefore, the
kfree_skb_reason() is involved at each "goto drop" to help userspace
ftrace/ebpf to track the reason for the loss of packets.
The below reasons are introduced:
- SKB_DROP_REASON_SKB_CSUM
- SKB_DROP_REASON_SKB_COPY_DATA
- SKB_DROP_REASON_SKB_GSO_SEG
- SKB_DROP_REASON_DEV_HDR
- SKB_DROP_REASON_FULL_RING
Cc: Joao Martins <[email protected]>
Cc: Joe Jin <[email protected]>
Signed-off-by: Dongli Zhang <[email protected]>
---
Changed since v1:
- revise the reason name
Changed since v2:
- declare drop_reason as type "enum skb_drop_reason"
- handle the drop in skb_list_walk_safe() case
drivers/net/tap.c | 35 +++++++++++++++++++++++++----------
include/linux/skbuff.h | 9 +++++++++
include/trace/events/skb.h | 5 +++++
3 files changed, 39 insertions(+), 10 deletions(-)
diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 8e3a28b..b48f519 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -322,6 +322,7 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
struct tap_dev *tap;
struct tap_queue *q;
netdev_features_t features = TAP_FEATURES;
+ enum skb_drop_reason drop_reason;
tap = tap_dev_get_rcu(dev);
if (!tap)
@@ -343,12 +344,16 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
struct sk_buff *segs = __skb_gso_segment(skb, features, false);
struct sk_buff *next;
- if (IS_ERR(segs))
+ if (IS_ERR(segs)) {
+ drop_reason = SKB_DROP_REASON_SKB_GSO_SEG;
goto drop;
+ }
if (!segs) {
- if (ptr_ring_produce(&q->ring, skb))
+ if (ptr_ring_produce(&q->ring, skb)) {
+ drop_reason = SKB_DROP_REASON_FULL_RING;
goto drop;
+ }
goto wake_up;
}
@@ -356,8 +361,9 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
skb_list_walk_safe(segs, skb, next) {
skb_mark_not_on_list(skb);
if (ptr_ring_produce(&q->ring, skb)) {
- kfree_skb(skb);
- kfree_skb_list(next);
+ drop_reason = SKB_DROP_REASON_FULL_RING;
+ kfree_skb_reason(skb, drop_reason);
+ kfree_skb_list_reason(next, drop_reason);
break;
}
}
@@ -369,10 +375,14 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
*/
if (skb->ip_summed == CHECKSUM_PARTIAL &&
!(features & NETIF_F_CSUM_MASK) &&
- skb_checksum_help(skb))
+ skb_checksum_help(skb)) {
+ drop_reason = SKB_DROP_REASON_SKB_CSUM;
goto drop;
- if (ptr_ring_produce(&q->ring, skb))
+ }
+ if (ptr_ring_produce(&q->ring, skb)) {
+ drop_reason = SKB_DROP_REASON_FULL_RING;
goto drop;
+ }
}
wake_up:
@@ -383,7 +393,7 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
/* Count errors/drops only here, thus don't care about args. */
if (tap->count_rx_dropped)
tap->count_rx_dropped(tap);
- kfree_skb(skb);
+ kfree_skb_reason(skb, drop_reason);
return RX_HANDLER_CONSUMED;
}
EXPORT_SYMBOL_GPL(tap_handle_frame);
@@ -632,6 +642,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
int depth;
bool zerocopy = false;
size_t linear;
+ enum skb_drop_reason drop_reason;
if (q->flags & IFF_VNET_HDR) {
vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
@@ -696,8 +707,10 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
else
err = skb_copy_datagram_from_iter(skb, 0, from, len);
- if (err)
+ if (err) {
+ drop_reason = SKB_DROP_REASON_SKB_COPY_DATA;
goto err_kfree;
+ }
skb_set_network_header(skb, ETH_HLEN);
skb_reset_mac_header(skb);
@@ -706,8 +719,10 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
if (vnet_hdr_len) {
err = virtio_net_hdr_to_skb(skb, &vnet_hdr,
tap_is_little_endian(q));
- if (err)
+ if (err) {
+ drop_reason = SKB_DROP_REASON_DEV_HDR;
goto err_kfree;
+ }
}
skb_probe_transport_header(skb);
@@ -738,7 +753,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
return total_len;
err_kfree:
- kfree_skb(skb);
+ kfree_skb_reason(skb, drop_reason);
err:
rcu_read_lock();
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 87ebe2f..52550c7 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -380,6 +380,15 @@ enum skb_drop_reason {
* the ofo queue, corresponding to
* LINUX_MIB_TCPOFOMERGE
*/
+ SKB_DROP_REASON_SKB_CSUM, /* sk_buff checksum error */
+ SKB_DROP_REASON_SKB_COPY_DATA, /* failed to copy data from or to
+ * sk_buff
+ */
+ SKB_DROP_REASON_SKB_GSO_SEG, /* gso segmentation error */
+ SKB_DROP_REASON_DEV_HDR, /* there is something wrong with
+ * device driver specific header
+ */
+ SKB_DROP_REASON_FULL_RING, /* ring buffer is full */
SKB_DROP_REASON_MAX,
};
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index 2ab7193..5b5f135 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -37,6 +37,11 @@
EM(SKB_DROP_REASON_TCP_OLD_DATA, TCP_OLD_DATA) \
EM(SKB_DROP_REASON_TCP_OVERWINDOW, TCP_OVERWINDOW) \
EM(SKB_DROP_REASON_TCP_OFOMERGE, TCP_OFOMERGE) \
+ EM(SKB_DROP_REASON_SKB_CSUM, SKB_CSUM) \
+ EM(SKB_DROP_REASON_SKB_COPY_DATA, SKB_COPY_DATA) \
+ EM(SKB_DROP_REASON_SKB_GSO_SEG, SKB_GSO_SEG) \
+ EM(SKB_DROP_REASON_DEV_HDR, DEV_HDR) \
+ EM(SKB_DROP_REASON_FULL_RING, FULL_RING) \
EMe(SKB_DROP_REASON_MAX, MAX)
#undef EM
--
1.8.3.1
On 2/20/22 10:34 PM, Dongli Zhang wrote:
> The TAP can be used as vhost-net backend. E.g., the tap_handle_frame() is
> the interface to forward the skb from TAP to vhost-net/virtio-net.
>
> However, there are many "goto drop" in the TAP driver. Therefore, the
> kfree_skb_reason() is involved at each "goto drop" to help userspace
> ftrace/ebpf to track the reason for the loss of packets.
>
> The below reasons are introduced:
>
> - SKB_DROP_REASON_SKB_CSUM
> - SKB_DROP_REASON_SKB_COPY_DATA
> - SKB_DROP_REASON_SKB_GSO_SEG
> - SKB_DROP_REASON_DEV_HDR
> - SKB_DROP_REASON_FULL_RING
>
> Cc: Joao Martins <[email protected]>
> Cc: Joe Jin <[email protected]>
> Signed-off-by: Dongli Zhang <[email protected]>
> ---
> Changed since v1:
> - revise the reason name
> Changed since v2:
> - declare drop_reason as type "enum skb_drop_reason"
> - handle the drop in skb_list_walk_safe() case
>
> drivers/net/tap.c | 35 +++++++++++++++++++++++++----------
> include/linux/skbuff.h | 9 +++++++++
> include/trace/events/skb.h | 5 +++++
> 3 files changed, 39 insertions(+), 10 deletions(-)
>
couple of places where the new reason should be in reverse xmas order;
logic wise:
Reviewed-by: David Ahern <[email protected]>
Hi David,
On 2/21/22 7:24 PM, David Ahern wrote:
> On 2/20/22 10:34 PM, Dongli Zhang wrote:
>> The TAP can be used as vhost-net backend. E.g., the tap_handle_frame() is
>> the interface to forward the skb from TAP to vhost-net/virtio-net.
>>
>> However, there are many "goto drop" in the TAP driver. Therefore, the
>> kfree_skb_reason() is involved at each "goto drop" to help userspace
>> ftrace/ebpf to track the reason for the loss of packets.
>>
>> The below reasons are introduced:
>>
>> - SKB_DROP_REASON_SKB_CSUM
>> - SKB_DROP_REASON_SKB_COPY_DATA
>> - SKB_DROP_REASON_SKB_GSO_SEG
>> - SKB_DROP_REASON_DEV_HDR
>> - SKB_DROP_REASON_FULL_RING
>>
>> Cc: Joao Martins <[email protected]>
>> Cc: Joe Jin <[email protected]>
>> Signed-off-by: Dongli Zhang <[email protected]>
>> ---
>> Changed since v1:
>> - revise the reason name
>> Changed since v2:
>> - declare drop_reason as type "enum skb_drop_reason"
>> - handle the drop in skb_list_walk_safe() case
>>
>> drivers/net/tap.c | 35 +++++++++++++++++++++++++----------
>> include/linux/skbuff.h | 9 +++++++++
>> include/trace/events/skb.h | 5 +++++
>> 3 files changed, 39 insertions(+), 10 deletions(-)
>>
>
> couple of places where the new reason should be in reverse xmas order;
> logic wise:
>
> Reviewed-by: David Ahern <[email protected]>
>
I will re-order the reasons in the same patch and re-send with your Reviewed-by
in the next version.
Thank you very much!
Dongli Zhang
On 2/21/22 8:31 PM, Dongli Zhang wrote:
> Hi David,
>
> On 2/21/22 7:24 PM, David Ahern wrote:
>> On 2/20/22 10:34 PM, Dongli Zhang wrote:
>>> The TAP can be used as vhost-net backend. E.g., the tap_handle_frame() is
>>> the interface to forward the skb from TAP to vhost-net/virtio-net.
>>>
>>> However, there are many "goto drop" in the TAP driver. Therefore, the
>>> kfree_skb_reason() is involved at each "goto drop" to help userspace
>>> ftrace/ebpf to track the reason for the loss of packets.
>>>
>>> The below reasons are introduced:
>>>
>>> - SKB_DROP_REASON_SKB_CSUM
>>> - SKB_DROP_REASON_SKB_COPY_DATA
>>> - SKB_DROP_REASON_SKB_GSO_SEG
>>> - SKB_DROP_REASON_DEV_HDR
>>> - SKB_DROP_REASON_FULL_RING
>>>
>>> Cc: Joao Martins <[email protected]>
>>> Cc: Joe Jin <[email protected]>
>>> Signed-off-by: Dongli Zhang <[email protected]>
>>> ---
>>> Changed since v1:
>>> - revise the reason name
>>> Changed since v2:
>>> - declare drop_reason as type "enum skb_drop_reason"
>>> - handle the drop in skb_list_walk_safe() case
>>>
>>> drivers/net/tap.c | 35 +++++++++++++++++++++++++----------
>>> include/linux/skbuff.h | 9 +++++++++
>>> include/trace/events/skb.h | 5 +++++
>>> 3 files changed, 39 insertions(+), 10 deletions(-)
>>>
>>
>> couple of places where the new reason should be in reverse xmas order;
>> logic wise:
>>
>> Reviewed-by: David Ahern <[email protected]>
>>
>
> I will re-order the reasons in the same patch and re-send with your Reviewed-by
> in the next version.
>
I have sent out v4 and I finally decide to not re-order reasons for this patch
as this may makes trouble for backport.
I will not follow the reverse xmas order here, as all existing variables are not
declared in reverse xmas order.
Thank you very much!
Dongli Zhang