[PATCH net-next v3 0/3] tun/tap: use kfree_skb_reason() to trace dropped skb

[PATCH net-next v3 0/3] tun/tap: use kfree_skb_reason() to trace dropped skb

[Dongli Zhang]

The commit c504e5c2f964 ("net: skb: introduce kfree_skb_reason()") has
introduced the kfree_skb_reason() to help track the reason.

The tun and tap are commonly used as virtio-net/vhost-net backend. This is to
use kfree_skb_reason() to trace the dropped skb for those two drivers. 

Changed since v1:
- I have renamed many of the reasons since v1. I make them as generic as
  possible so that they can be re-used by core networking and drivers.

Changed since v2:
- declare drop_reason as type "enum skb_drop_reason"
- handle the drop in skb_list_walk_safe() case for tap driver, and
  kfree_skb_list_reason() is introduced


The following reasons are introduced.

- SKB_DROP_REASON_SKB_CSUM

This is used whenever there is checksum error with sk_buff.

- SKB_DROP_REASON_SKB_COPY_DATA

The kernel may (zero) copy the data to or from sk_buff, e.g.,
zerocopy_sg_from_iter(), skb_copy_datagram_from_iter() and
skb_orphan_frags_rx(). This reason is for the copy related error.

- SKB_DROP_REASON_SKB_GSO_SEG

Any error reported when GSO processing the sk_buff. It is frequent to process
sk_buff gso data and we introduce a new reason to handle that.
	
- SKB_DROP_REASON_SKB_PULL
- SKB_DROP_REASON_SKB_TRIM

It is frequent to pull to sk_buff data or trim the sk_buff data.

- SKB_DROP_REASON_DEV_HDR

Any driver may report error if there is any error in the metadata on the DMA
ring buffer.

- SKB_DROP_REASON_DEV_READY

The device is not ready/online or initialized to receive data.

- SKB_DROP_REASON_DEV_FILTER

David Ahern suggested SKB_DROP_REASON_TAP_FILTER. I changed from 'TAP' to 'DEV'
to make it more generic.

- SKB_DROP_REASON_FULL_RING

Suggested by Eric Dumazet.

- SKB_DROP_REASON_BPF_FILTER

Dropped by ebpf filter


This is the output for TUN device.

# cat /sys/kernel/debug/tracing/trace_pipe
          <idle>-0       [018] ..s1.  1478.130490: kfree_skb: skbaddr=00000000c4f21b8d protocol=0 location=00000000aff342c7 reason: NOT_SPECIFIED
      vhost-9003-9020    [012] b..1.  1478.196264: kfree_skb: skbaddr=00000000b174fb9b protocol=2054 location=000000001cf38db0 reason: FULL_RING
          arping-9639    [018] b..1.  1479.082993: kfree_skb: skbaddr=00000000c4f21b8d protocol=2054 location=000000001cf38db0 reason: FULL_RING
          <idle>-0       [012] b.s3.  1479.110472: kfree_skb: skbaddr=00000000e0c3681f protocol=4 location=000000001cf38db0 reason: FULL_RING
          arping-9639    [018] b..1.  1480.083086: kfree_skb: skbaddr=00000000c4f21b8d protocol=2054 location=000000001cf38db0 reason: FULL_RING


This is the output for TAP device.

# cat /sys/kernel/debug/tracing/trace_pipe
          <idle>-0       [014] ..s1.  1096.418621: kfree_skb: skbaddr=00000000f8f41946 protocol=0 location=00000000aff342c7 reason: NOT_SPECIFIED
          arping-7006    [001] ..s1.  1096.843961: kfree_skb: skbaddr=000000002ec803a8 protocol=2054 location=000000009a57b32f reason: FULL_RING
          arping-7006    [001] ..s1.  1097.844035: kfree_skb: skbaddr=000000002ec803a8 protocol=2054 location=000000009a57b32f reason: FULL_RING
          arping-7006    [001] ..s1.  1098.844102: kfree_skb: skbaddr=00000000295eb0da protocol=2054 location=000000009a57b32f reason: FULL_RING
          arping-7006    [001] ..s1.  1099.844160: kfree_skb: skbaddr=00000000295eb0da protocol=2054 location=000000009a57b32f reason: FULL_RING
          arping-7006    [001] ..s1.  1100.844214: kfree_skb: skbaddr=00000000295eb0da protocol=2054 location=000000009a57b32f reason: FULL_RING
          arping-7006    [001] ..s1.  1101.844230: kfree_skb: skbaddr=00000000295eb0da protocol=2054 location=000000009a57b32f reason: FULL_RING


 drivers/net/tap.c          | 35 +++++++++++++++++++++++++----------
 drivers/net/tun.c          | 38 ++++++++++++++++++++++++++++++--------
 include/linux/skbuff.h     | 18 ++++++++++++++++++
 include/trace/events/skb.h | 10 ++++++++++
 net/core/skbuff.c          | 11 +++++++++--
 5 files changed, 92 insertions(+), 20 deletions(-)

Please let me know if there is any suggestion on the definition of reasons.

Thank you very much!

Dongli Zhang

[PATCH net-next v3 1/4] skbuff: introduce kfree_skb_list_reason()

[Dongli Zhang]

This is to introduce kfree_skb_list_reason() to drop a list of sk_buff with
a specific reason.

Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
 include/linux/skbuff.h |  2 ++
 net/core/skbuff.c      | 11 +++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index a3e90ef..87ebe2f 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1176,6 +1176,8 @@ static inline void kfree_skb(struct sk_buff *skb)
 }
 
 void skb_release_head_state(struct sk_buff *skb);
+void kfree_skb_list_reason(struct sk_buff *segs,
+			   enum skb_drop_reason reason);
 void kfree_skb_list(struct sk_buff *segs);
 void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt);
 void skb_tx_error(struct sk_buff *skb);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 9d0388be..dfdd71e 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -777,15 +777,22 @@ void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
 }
 EXPORT_SYMBOL(kfree_skb_reason);
 
-void kfree_skb_list(struct sk_buff *segs)
+void kfree_skb_list_reason(struct sk_buff *segs,
+			   enum skb_drop_reason reason)
 {
 	while (segs) {
 		struct sk_buff *next = segs->next;
 
-		kfree_skb(segs);
+		kfree_skb_reason(segs, reason);
 		segs = next;
 	}
 }
+EXPORT_SYMBOL(kfree_skb_list_reason);
+
+void kfree_skb_list(struct sk_buff *segs)
+{
+	kfree_skb_list_reason(segs, SKB_DROP_REASON_NOT_SPECIFIED);
+}
 EXPORT_SYMBOL(kfree_skb_list);
 
 /* Dump skb information and contents.
-- 
1.8.3.1

Re: [PATCH net-next v3 1/4] skbuff: introduce kfree_skb_list_reason()

[David Ahern]

On 2/20/22 10:34 PM, Dongli Zhang wrote:
> This is to introduce kfree_skb_list_reason() to drop a list of sk_buff with
> a specific reason.
> 
> Cc: Joao Martins <joao.m.martins@oracle.com>
> Cc: Joe Jin <joe.jin@oracle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
>  include/linux/skbuff.h |  2 ++
>  net/core/skbuff.c      | 11 +++++++++--
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
>

Reviewed-by: David Ahern <dsahern@kernel.org>

[PATCH net-next v3 2/4] net: tap: track dropped skb via kfree_skb_reason()

[Dongli Zhang]

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 <joao.m.martins@oracle.com>
Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
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

Re: [PATCH net-next v3 2/4] net: tap: track dropped skb via kfree_skb_reason()

[David Ahern]

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 <joao.m.martins@oracle.com>
> Cc: Joe Jin <joe.jin@oracle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
> 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 <dsahern@kernel.org>

Re: [PATCH net-next v3 2/4] net: tap: track dropped skb via kfree_skb_reason()

[Dongli Zhang]

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 <joao.m.martins@oracle.com>
>> Cc: Joe Jin <joe.jin@oracle.com>
>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
>> ---
>> 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 <dsahern@kernel.org>
> 

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

Re: [PATCH net-next v3 2/4] net: tap: track dropped skb via kfree_skb_reason()

[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 <joao.m.martins@oracle.com>
>>> Cc: Joe Jin <joe.jin@oracle.com>
>>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
>>> ---
>>> 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 <dsahern@kernel.org>
>>
> 
> 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

[PATCH net-next v3 3/4] net: tun: split run_ebpf_filter() and pskb_trim() into different "if statement"

[Dongli Zhang]

No functional change.

Just to split the if statement into different conditions to use
kfree_skb_reason() to trace the reason later.

Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
 drivers/net/tun.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index fed8544..aa27268 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1086,7 +1086,10 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto drop;
 
 	len = run_ebpf_filter(tun, skb, len);
-	if (len == 0 || pskb_trim(skb, len))
+	if (len == 0)
+		goto drop;
+
+	if (pskb_trim(skb, len))
 		goto drop;
 
 	if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC)))
-- 
1.8.3.1

Re: [PATCH net-next v3 3/4] net: tun: split run_ebpf_filter() and pskb_trim() into different "if statement"

[David Ahern]

On 2/20/22 10:34 PM, Dongli Zhang wrote:
> No functional change.
> 
> Just to split the if statement into different conditions to use
> kfree_skb_reason() to trace the reason later.
> 
> Cc: Joao Martins <joao.m.martins@oracle.com>
> Cc: Joe Jin <joe.jin@oracle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
>  drivers/net/tun.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>

[PATCH net-next v3 4/4] net: tun: track dropped skb via kfree_skb_reason()

[Dongli Zhang]

The TUN can be used as vhost-net backend. E.g, the tun_net_xmit() is the
interface to forward the skb from TUN to vhost-net/virtio-net.

However, there are many "goto drop" in the TUN 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_PULL
- SKB_DROP_REASON_SKB_TRIM
- SKB_DROP_REASON_DEV_READY
- SKB_DROP_REASON_DEV_FILTER
- SKB_DROP_REASON_BPF_FILTER

Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
Changed since v1:
- revise the reason name
Changed since v2:
- declare drop_reason as type "enum skb_drop_reason"

 drivers/net/tun.c          | 37 ++++++++++++++++++++++++++++---------
 include/linux/skbuff.h     |  7 +++++++
 include/trace/events/skb.h |  5 +++++
 3 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index aa27268..bf7d8cd 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1062,13 +1062,16 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct netdev_queue *queue;
 	struct tun_file *tfile;
 	int len = skb->len;
+	enum skb_drop_reason drop_reason;
 
 	rcu_read_lock();
 	tfile = rcu_dereference(tun->tfiles[txq]);
 
 	/* Drop packet if interface is not attached */
-	if (!tfile)
+	if (!tfile) {
+		drop_reason = SKB_DROP_REASON_DEV_READY;
 		goto drop;
+	}
 
 	if (!rcu_dereference(tun->steering_prog))
 		tun_automq_xmit(tun, skb);
@@ -1078,22 +1081,32 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* Drop if the filter does not like it.
 	 * This is a noop if the filter is disabled.
 	 * Filter can be enabled only for the TAP devices. */
-	if (!check_filter(&tun->txflt, skb))
+	if (!check_filter(&tun->txflt, skb)) {
+		drop_reason = SKB_DROP_REASON_DEV_FILTER;
 		goto drop;
+	}
 
 	if (tfile->socket.sk->sk_filter &&
-	    sk_filter(tfile->socket.sk, skb))
+	    sk_filter(tfile->socket.sk, skb)) {
+		drop_reason = SKB_DROP_REASON_SOCKET_FILTER;
 		goto drop;
+	}
 
 	len = run_ebpf_filter(tun, skb, len);
-	if (len == 0)
+	if (len == 0) {
+		drop_reason = SKB_DROP_REASON_BPF_FILTER;
 		goto drop;
+	}
 
-	if (pskb_trim(skb, len))
+	if (pskb_trim(skb, len)) {
+		drop_reason = SKB_DROP_REASON_SKB_TRIM;
 		goto drop;
+	}
 
-	if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC)))
+	if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC))) {
+		drop_reason = SKB_DROP_REASON_SKB_COPY_DATA;
 		goto drop;
+	}
 
 	skb_tx_timestamp(skb);
 
@@ -1104,8 +1117,10 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	nf_reset_ct(skb);
 
-	if (ptr_ring_produce(&tfile->tx_ring, skb))
+	if (ptr_ring_produce(&tfile->tx_ring, skb)) {
+		drop_reason = SKB_DROP_REASON_FULL_RING;
 		goto drop;
+	}
 
 	/* NETIF_F_LLTX requires to do our own update of trans_start */
 	queue = netdev_get_tx_queue(dev, txq);
@@ -1122,7 +1137,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 drop:
 	atomic_long_inc(&dev->tx_dropped);
 	skb_tx_error(skb);
-	kfree_skb(skb);
+	kfree_skb_reason(skb, drop_reason);
 	rcu_read_unlock();
 	return NET_XMIT_DROP;
 }
@@ -1720,6 +1735,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	u32 rxhash = 0;
 	int skb_xdp = 1;
 	bool frags = tun_napi_frags_enabled(tfile);
+	enum skb_drop_reason drop_reason;
 
 	if (!(tun->flags & IFF_NO_PI)) {
 		if (len < sizeof(pi))
@@ -1823,9 +1839,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 
 		if (err) {
 			err = -EFAULT;
+			drop_reason = SKB_DROP_REASON_SKB_COPY_DATA;
 drop:
 			atomic_long_inc(&tun->dev->rx_dropped);
-			kfree_skb(skb);
+			kfree_skb_reason(skb, drop_reason);
 			if (frags) {
 				tfile->napi.skb = NULL;
 				mutex_unlock(&tfile->napi_mutex);
@@ -1872,6 +1889,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	case IFF_TAP:
 		if (frags && !pskb_may_pull(skb, ETH_HLEN)) {
 			err = -ENOMEM;
+			drop_reason = SKB_DROP_REASON_SKB_PULL;
 			goto drop;
 		}
 		skb->protocol = eth_type_trans(skb, tun->dev);
@@ -1925,6 +1943,7 @@ 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();
+		drop_reason = SKB_DROP_REASON_DEV_READY;
 		goto drop;
 	}
 
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 52550c7..5850590 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -385,10 +385,17 @@ enum skb_drop_reason {
 					 * sk_buff
 					 */
 	SKB_DROP_REASON_SKB_GSO_SEG,	/* gso segmentation error */
+	SKB_DROP_REASON_SKB_PULL,	/* failed to pull sk_buff data */
+	SKB_DROP_REASON_SKB_TRIM,	/* failed to trim sk_buff data */
 	SKB_DROP_REASON_DEV_HDR,	/* there is something wrong with
 					 * device driver specific header
 					 */
+	SKB_DROP_REASON_DEV_READY,	/* device is not ready */
+	SKB_DROP_REASON_DEV_FILTER,	/* dropped by device driver
+					 * specific filter
+					 */
 	SKB_DROP_REASON_FULL_RING,	/* ring buffer is full */
+	SKB_DROP_REASON_BPF_FILTER,	/* dropped by ebpf filter */
 	SKB_DROP_REASON_MAX,
 };
 
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index 5b5f135..0db0962 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -40,8 +40,13 @@
 	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_SKB_PULL, SKB_PULL)			\
+	EM(SKB_DROP_REASON_SKB_TRIM, SKB_TRIM)			\
 	EM(SKB_DROP_REASON_DEV_HDR, DEV_HDR)			\
+	EM(SKB_DROP_REASON_DEV_READY, DEV_READY)		\
+	EM(SKB_DROP_REASON_DEV_FILTER, DEV_FILTER)		\
 	EM(SKB_DROP_REASON_FULL_RING, FULL_RING)		\
+	EM(SKB_DROP_REASON_BPF_FILTER, BPF_FILTER)		\
 	EMe(SKB_DROP_REASON_MAX, MAX)
 
 #undef EM
-- 
1.8.3.1

Re: [PATCH net-next v3 4/4] net: tun: track dropped skb via kfree_skb_reason()

[David Ahern]

On 2/20/22 10:34 PM, Dongli Zhang wrote:
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index aa27268..bf7d8cd 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1062,13 +1062,16 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>  	struct netdev_queue *queue;
>  	struct tun_file *tfile;
>  	int len = skb->len;
> +	enum skb_drop_reason drop_reason;

this function is already honoring reverse xmas tree style, so this needs
to be moved up.

>  
>  	rcu_read_lock();
>  	tfile = rcu_dereference(tun->tfiles[txq]);
>  
>  	/* Drop packet if interface is not attached */
> -	if (!tfile)
> +	if (!tfile) {
> +		drop_reason = SKB_DROP_REASON_DEV_READY;
>  		goto drop;
> +	}
>  
>  	if (!rcu_dereference(tun->steering_prog))
>  		tun_automq_xmit(tun, skb);
> @@ -1078,22 +1081,32 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>  	/* Drop if the filter does not like it.
>  	 * This is a noop if the filter is disabled.
>  	 * Filter can be enabled only for the TAP devices. */
> -	if (!check_filter(&tun->txflt, skb))
> +	if (!check_filter(&tun->txflt, skb)) {
> +		drop_reason = SKB_DROP_REASON_DEV_FILTER;
>  		goto drop;
> +	}
>  
>  	if (tfile->socket.sk->sk_filter &&
> -	    sk_filter(tfile->socket.sk, skb))
> +	    sk_filter(tfile->socket.sk, skb)) {
> +		drop_reason = SKB_DROP_REASON_SOCKET_FILTER;
>  		goto drop;
> +	}
>  
>  	len = run_ebpf_filter(tun, skb, len);
> -	if (len == 0)
> +	if (len == 0) {
> +		drop_reason = SKB_DROP_REASON_BPF_FILTER;

how does this bpf filter differ from SKB_DROP_REASON_SOCKET_FILTER? I
think the reason code needs to be a little clearer on the distinction.

Re: [PATCH net-next v3 4/4] net: tun: track dropped skb via kfree_skb_reason()

[Dongli Zhang]

Hi David,

On 2/21/22 7:28 PM, David Ahern wrote:
> On 2/20/22 10:34 PM, Dongli Zhang wrote:
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index aa27268..bf7d8cd 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -1062,13 +1062,16 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>  	struct netdev_queue *queue;
>>  	struct tun_file *tfile;
>>  	int len = skb->len;
>> +	enum skb_drop_reason drop_reason;
> 
> this function is already honoring reverse xmas tree style, so this needs
> to be moved up.

I will move this up to before "int txq = skb->queue_mapping;".

> 
>>  
>>  	rcu_read_lock();
>>  	tfile = rcu_dereference(tun->tfiles[txq]);
>>  
>>  	/* Drop packet if interface is not attached */
>> -	if (!tfile)
>> +	if (!tfile) {
>> +		drop_reason = SKB_DROP_REASON_DEV_READY;
>>  		goto drop;
>> +	}
>>  
>>  	if (!rcu_dereference(tun->steering_prog))
>>  		tun_automq_xmit(tun, skb);
>> @@ -1078,22 +1081,32 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>  	/* Drop if the filter does not like it.
>>  	 * This is a noop if the filter is disabled.
>>  	 * Filter can be enabled only for the TAP devices. */
>> -	if (!check_filter(&tun->txflt, skb))
>> +	if (!check_filter(&tun->txflt, skb)) {
>> +		drop_reason = SKB_DROP_REASON_DEV_FILTER;
>>  		goto drop;
>> +	}
>>  
>>  	if (tfile->socket.sk->sk_filter &&
>> -	    sk_filter(tfile->socket.sk, skb))
>> +	    sk_filter(tfile->socket.sk, skb)) {
>> +		drop_reason = SKB_DROP_REASON_SOCKET_FILTER;
>>  		goto drop;
>> +	}
>>  
>>  	len = run_ebpf_filter(tun, skb, len);
>> -	if (len == 0)
>> +	if (len == 0) {
>> +		drop_reason = SKB_DROP_REASON_BPF_FILTER;
> 
> how does this bpf filter differ from SKB_DROP_REASON_SOCKET_FILTER? I
> think the reason code needs to be a little clearer on the distinction.
> 


While there is a diff between BPF_FILTER (here) and SOCKET_FILTER ...

... indeed the issue is: there is NO diff between BPF_FILTER (here) and
DEV_FILTER (introduced by the patch).


The run_ebpf_filter() is to run the bpf filter attached to the TUN device (not
socket). This is similar to DEV_FILTER, which is to run a device specific filter.

Initially, I would use DEV_FILTER at both locations. This makes trouble to me as
there would be two places with same reason=DEV_FILTER. I will not be able to
tell where the skb is dropped.


I was thinking about to introduce a SKB_DROP_REASON_DEV_BPF. While I have
limited experience in device specific bpf, the TUN is the only device I know
that has a device specific ebpf filter (by commit aff3d70a07ff ("tun: allow to
attach ebpf socket filter")). The SKB_DROP_REASON_DEV_BPF is not generic enough
to be re-used by other drivers.


Would you mind sharing your suggestion if I would re-use (1)
SKB_DROP_REASON_DEV_FILTER or (2) introduce a new SKB_DROP_REASON_DEV_BPF, which
is for sk_buff dropped by ebpf attached to device (not socket).


To answer your question, the SOCKET_FILTER is for filter attached to socket, the
BPF_FILTER was supposed for ebpf filter attached to device (tun->filter_prog).


Thank you very much!

Dongli Zhang

Re: [PATCH net-next v3 4/4] net: tun: track dropped skb via kfree_skb_reason()

[David Ahern]

On 2/21/22 9:45 PM, Dongli Zhang wrote:
> Hi David,
> 
> On 2/21/22 7:28 PM, David Ahern wrote:
>> On 2/20/22 10:34 PM, Dongli Zhang wrote:
>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>> index aa27268..bf7d8cd 100644
>>> --- a/drivers/net/tun.c
>>> +++ b/drivers/net/tun.c
>>> @@ -1062,13 +1062,16 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>>  	struct netdev_queue *queue;
>>>  	struct tun_file *tfile;
>>>  	int len = skb->len;
>>> +	enum skb_drop_reason drop_reason;
>>
>> this function is already honoring reverse xmas tree style, so this needs
>> to be moved up.
> 
> I will move this up to before "int txq = skb->queue_mapping;".
> 
>>
>>>  
>>>  	rcu_read_lock();
>>>  	tfile = rcu_dereference(tun->tfiles[txq]);
>>>  
>>>  	/* Drop packet if interface is not attached */
>>> -	if (!tfile)
>>> +	if (!tfile) {
>>> +		drop_reason = SKB_DROP_REASON_DEV_READY;
>>>  		goto drop;
>>> +	}
>>>  
>>>  	if (!rcu_dereference(tun->steering_prog))
>>>  		tun_automq_xmit(tun, skb);
>>> @@ -1078,22 +1081,32 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>>  	/* Drop if the filter does not like it.
>>>  	 * This is a noop if the filter is disabled.
>>>  	 * Filter can be enabled only for the TAP devices. */
>>> -	if (!check_filter(&tun->txflt, skb))
>>> +	if (!check_filter(&tun->txflt, skb)) {
>>> +		drop_reason = SKB_DROP_REASON_DEV_FILTER;
>>>  		goto drop;
>>> +	}
>>>  
>>>  	if (tfile->socket.sk->sk_filter &&
>>> -	    sk_filter(tfile->socket.sk, skb))
>>> +	    sk_filter(tfile->socket.sk, skb)) {
>>> +		drop_reason = SKB_DROP_REASON_SOCKET_FILTER;
>>>  		goto drop;
>>> +	}
>>>  
>>>  	len = run_ebpf_filter(tun, skb, len);
>>> -	if (len == 0)
>>> +	if (len == 0) {
>>> +		drop_reason = SKB_DROP_REASON_BPF_FILTER;
>>
>> how does this bpf filter differ from SKB_DROP_REASON_SOCKET_FILTER? I
>> think the reason code needs to be a little clearer on the distinction.
>>
> 
> 
> While there is a diff between BPF_FILTER (here) and SOCKET_FILTER ...
> 
> ... indeed the issue is: there is NO diff between BPF_FILTER (here) and
> DEV_FILTER (introduced by the patch).
> 
> 
> The run_ebpf_filter() is to run the bpf filter attached to the TUN device (not
> socket). This is similar to DEV_FILTER, which is to run a device specific filter.
> 
> Initially, I would use DEV_FILTER at both locations. This makes trouble to me as
> there would be two places with same reason=DEV_FILTER. I will not be able to
> tell where the skb is dropped.
> 
> 
> I was thinking about to introduce a SKB_DROP_REASON_DEV_BPF. While I have
> limited experience in device specific bpf, the TUN is the only device I know
> that has a device specific ebpf filter (by commit aff3d70a07ff ("tun: allow to
> attach ebpf socket filter")). The SKB_DROP_REASON_DEV_BPF is not generic enough
> to be re-used by other drivers.
> 
> 
> Would you mind sharing your suggestion if I would re-use (1)
> SKB_DROP_REASON_DEV_FILTER or (2) introduce a new SKB_DROP_REASON_DEV_BPF, which
> is for sk_buff dropped by ebpf attached to device (not socket).
> 
> 
> To answer your question, the SOCKET_FILTER is for filter attached to socket, the
> BPF_FILTER was supposed for ebpf filter attached to device (tun->filter_prog).
> 
> 

tun/tap does have some unique filtering options. The other sets focused
on the core networking stack is adding a drop reason of
SKB_DROP_REASON_BPF_CGROUP_EGRESS for cgroup based egress filters.

For tun unique filters, how about using a shortened version of the ioctl
name used to set the filter.

Re: [PATCH net-next v3 4/4] net: tun: track dropped skb via kfree_skb_reason()

[Dongli Zhang]

Hi David,

On 2/22/22 6:39 AM, David Ahern wrote:
> On 2/21/22 9:45 PM, Dongli Zhang wrote:
>> Hi David,
>>
>> On 2/21/22 7:28 PM, David Ahern wrote:
>>> On 2/20/22 10:34 PM, Dongli Zhang wrote:
>>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>>> index aa27268..bf7d8cd 100644
>>>> --- a/drivers/net/tun.c
>>>> +++ b/drivers/net/tun.c
>>>> @@ -1062,13 +1062,16 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>>>  	struct netdev_queue *queue;
>>>>  	struct tun_file *tfile;
>>>>  	int len = skb->len;
>>>> +	enum skb_drop_reason drop_reason;
>>>
>>> this function is already honoring reverse xmas tree style, so this needs
>>> to be moved up.
>>
>> I will move this up to before "int txq = skb->queue_mapping;".
>>
>>>
>>>>  
>>>>  	rcu_read_lock();
>>>>  	tfile = rcu_dereference(tun->tfiles[txq]);
>>>>  
>>>>  	/* Drop packet if interface is not attached */
>>>> -	if (!tfile)
>>>> +	if (!tfile) {
>>>> +		drop_reason = SKB_DROP_REASON_DEV_READY;
>>>>  		goto drop;
>>>> +	}
>>>>  
>>>>  	if (!rcu_dereference(tun->steering_prog))
>>>>  		tun_automq_xmit(tun, skb);
>>>> @@ -1078,22 +1081,32 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>>>  	/* Drop if the filter does not like it.
>>>>  	 * This is a noop if the filter is disabled.
>>>>  	 * Filter can be enabled only for the TAP devices. */
>>>> -	if (!check_filter(&tun->txflt, skb))
>>>> +	if (!check_filter(&tun->txflt, skb)) {
>>>> +		drop_reason = SKB_DROP_REASON_DEV_FILTER;
>>>>  		goto drop;
>>>> +	}
>>>>  
>>>>  	if (tfile->socket.sk->sk_filter &&
>>>> -	    sk_filter(tfile->socket.sk, skb))
>>>> +	    sk_filter(tfile->socket.sk, skb)) {
>>>> +		drop_reason = SKB_DROP_REASON_SOCKET_FILTER;
>>>>  		goto drop;
>>>> +	}
>>>>  
>>>>  	len = run_ebpf_filter(tun, skb, len);
>>>> -	if (len == 0)
>>>> +	if (len == 0) {
>>>> +		drop_reason = SKB_DROP_REASON_BPF_FILTER;
>>>
>>> how does this bpf filter differ from SKB_DROP_REASON_SOCKET_FILTER? I
>>> think the reason code needs to be a little clearer on the distinction.
>>>
>>
>>
>> While there is a diff between BPF_FILTER (here) and SOCKET_FILTER ...
>>
>> ... indeed the issue is: there is NO diff between BPF_FILTER (here) and
>> DEV_FILTER (introduced by the patch).
>>
>>
>> The run_ebpf_filter() is to run the bpf filter attached to the TUN device (not
>> socket). This is similar to DEV_FILTER, which is to run a device specific filter.
>>
>> Initially, I would use DEV_FILTER at both locations. This makes trouble to me as
>> there would be two places with same reason=DEV_FILTER. I will not be able to
>> tell where the skb is dropped.
>>
>>
>> I was thinking about to introduce a SKB_DROP_REASON_DEV_BPF. While I have
>> limited experience in device specific bpf, the TUN is the only device I know
>> that has a device specific ebpf filter (by commit aff3d70a07ff ("tun: allow to
>> attach ebpf socket filter")). The SKB_DROP_REASON_DEV_BPF is not generic enough
>> to be re-used by other drivers.
>>
>>
>> Would you mind sharing your suggestion if I would re-use (1)
>> SKB_DROP_REASON_DEV_FILTER or (2) introduce a new SKB_DROP_REASON_DEV_BPF, which
>> is for sk_buff dropped by ebpf attached to device (not socket).
>>
>>
>> To answer your question, the SOCKET_FILTER is for filter attached to socket, the
>> BPF_FILTER was supposed for ebpf filter attached to device (tun->filter_prog).
>>
>>
> 
> tun/tap does have some unique filtering options. The other sets focused
> on the core networking stack is adding a drop reason of
> SKB_DROP_REASON_BPF_CGROUP_EGRESS for cgroup based egress filters.

Thank you for the explanation!

> 
> For tun unique filters, how about using a shortened version of the ioctl
> name used to set the filter.
> 

Although TUN is widely used in virtualization environment, it is only one of
many drivers. I prefer to not introduce a reason that can be used only by a
specific driver.

In order to make it more generic and more re-usable (e.g., perhaps people may
add ebpf filter to TAP driver as well), how about we create below reasons.

SKB_DROP_REASON_DEV_FILTER,     /* dropped by filter attached to
				 * or directly implemented by a
				 * specific driver
				 */
SKB_DROP_REASON_BPF_DEV,	/* dropped by bpf directly
				 * attached to a specific device,
				 * e.g., via TUNSETFILTEREBPF
				 */

We already use SKB_DROP_REASON_DEV_FILTER in this patchset. We will use
SKB_DROP_REASON_BPF_DEV for the ebpf filter attached to TUN.

Thank you very much!

Dongli Zhang

[PATCH net-next v3 4/4] net: tun: track dropped skb via kfree_skb_reason()

[Menglong Dong]

>Hi David,
>
>On 2/22/22 6:39 AM, David Ahern wrote:
>> On 2/21/22 9:45 PM, Dongli Zhang wrote:
>>> Hi David,
>>>
>>> On 2/21/22 7:28 PM, David Ahern wrote:
>>>> On 2/20/22 10:34 PM, Dongli Zhang wrote:
>>>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>>>> index aa27268..bf7d8cd 100644
>>>>> --- a/drivers/net/tun.c
>>>>> +++ b/drivers/net/tun.c
>>>>> @@ -1062,13 +1062,16 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>>>>  	struct netdev_queue *queue;
>>>>>  	struct tun_file *tfile;
>>>>>  	int len = skb->len;
>>>>> +	enum skb_drop_reason drop_reason;
>>>>
>>>> this function is already honoring reverse xmas tree style, so this needs
>>>> to be moved up.
>>>
>>> I will move this up to before "int txq = skb->queue_mapping;".
>>>
>>>>
[...]
>>>>
>>>
>>>
>>> While there is a diff between BPF_FILTER (here) and SOCKET_FILTER ...
>>>
>>> ... indeed the issue is: there is NO diff between BPF_FILTER (here) and
>>> DEV_FILTER (introduced by the patch).
>>>
>>>
>>> The run_ebpf_filter() is to run the bpf filter attached to the TUN device (not
>>> socket). This is similar to DEV_FILTER, which is to run a device specific filter.
>>>
>>> Initially, I would use DEV_FILTER at both locations. This makes trouble to me as
>>> there would be two places with same reason=DEV_FILTER. I will not be able to
>>> tell where the skb is dropped.
>>>
>>>
>>> I was thinking about to introduce a SKB_DROP_REASON_DEV_BPF. While I have
>>> limited experience in device specific bpf, the TUN is the only device I know
>>> that has a device specific ebpf filter (by commit aff3d70a07ff ("tun: allow to
>>> attach ebpf socket filter")). The SKB_DROP_REASON_DEV_BPF is not generic enough
>>> to be re-used by other drivers.
>>>
>>>
>>> Would you mind sharing your suggestion if I would re-use (1)
>>> SKB_DROP_REASON_DEV_FILTER or (2) introduce a new SKB_DROP_REASON_DEV_BPF, which
>>> is for sk_buff dropped by ebpf attached to device (not socket).
>>>
>>>
>>> To answer your question, the SOCKET_FILTER is for filter attached to socket, the
>>> BPF_FILTER was supposed for ebpf filter attached to device (tun->filter_prog).
>>>
>>>
>> 
>> tun/tap does have some unique filtering options. The other sets focused
>> on the core networking stack is adding a drop reason of
>> SKB_DROP_REASON_BPF_CGROUP_EGRESS for cgroup based egress filters.
>
>Thank you for the explanation!
>
>> 
>> For tun unique filters, how about using a shortened version of the ioctl
>> name used to set the filter.
>> 
>
>Although TUN is widely used in virtualization environment, it is only one of
>many drivers. I prefer to not introduce a reason that can be used only by a
>specific driver.
>
>In order to make it more generic and more re-usable (e.g., perhaps people may
>add ebpf filter to TAP driver as well), how about we create below reasons.
>
>SKB_DROP_REASON_DEV_FILTER,     /* dropped by filter attached to
>				 * or directly implemented by a
>				 * specific driver
>				 */
>SKB_DROP_REASON_BPF_DEV,	/* dropped by bpf directly
>				 * attached to a specific device,
>				 * e.g., via TUNSETFILTEREBPF
>				 */

Aren't DEV_FILTER and BPF_DEV too generic? eBPF atached to netdev can
be many kinds, such as XDP, TC, etc.

I think that use TAP_TXFILTER instaed of DEV_FILTER maybe better?
and TAP_FILTER->BPF_DEV. Make them similar to the name in
__tun_chr_ioctl() may be easier for user to understand.

>
>We already use SKB_DROP_REASON_DEV_FILTER in this patchset. We will use
>SKB_DROP_REASON_BPF_DEV for the ebpf filter attached to TUN.
>
>Thank you very much!
>
>Dongli Zhang

Re: [PATCH net-next v3 4/4] net: tun: track dropped skb via kfree_skb_reason()

[David Ahern]

On 2/24/22 10:57 PM, Menglong Dong wrote:
>>>
>>> For tun unique filters, how about using a shortened version of the ioctl
>>> name used to set the filter.
>>>
>>
>> Although TUN is widely used in virtualization environment, it is only one of
>> many drivers. I prefer to not introduce a reason that can be used only by a
>> specific driver.
>>
>> In order to make it more generic and more re-usable (e.g., perhaps people may
>> add ebpf filter to TAP driver as well), how about we create below reasons.
>>
>> SKB_DROP_REASON_DEV_FILTER,     /* dropped by filter attached to
>> 				 * or directly implemented by a
>> 				 * specific driver
>> 				 */
>> SKB_DROP_REASON_BPF_DEV,	/* dropped by bpf directly
>> 				 * attached to a specific device,
>> 				 * e.g., via TUNSETFILTEREBPF
>> 				 */
> 
> Aren't DEV_FILTER and BPF_DEV too generic? eBPF atached to netdev can
> be many kinds, such as XDP, TC, etc.

yes.

> 
> I think that use TAP_TXFILTER instaed of DEV_FILTER maybe better?
> and TAP_FILTER->BPF_DEV. Make them similar to the name in
> __tun_chr_ioctl() may be easier for user to understand.
> 

in this case given the unique attach points and API tap in the name
seems more appropriate

Re: [PATCH net-next v3 4/4] net: tun: track dropped skb via kfree_skb_reason()

[Dongli Zhang]

Hi David and Menglong,

On 2/25/22 7:48 AM, David Ahern wrote:
> On 2/24/22 10:57 PM, Menglong Dong wrote:
>>>>
>>>> For tun unique filters, how about using a shortened version of the ioctl
>>>> name used to set the filter.
>>>>
>>>
>>> Although TUN is widely used in virtualization environment, it is only one of
>>> many drivers. I prefer to not introduce a reason that can be used only by a
>>> specific driver.
>>>
>>> In order to make it more generic and more re-usable (e.g., perhaps people may
>>> add ebpf filter to TAP driver as well), how about we create below reasons.
>>>
>>> SKB_DROP_REASON_DEV_FILTER,     /* dropped by filter attached to
>>> 				 * or directly implemented by a
>>> 				 * specific driver
>>> 				 */
>>> SKB_DROP_REASON_BPF_DEV,	/* dropped by bpf directly
>>> 				 * attached to a specific device,
>>> 				 * e.g., via TUNSETFILTEREBPF
>>> 				 */
>>
>> Aren't DEV_FILTER and BPF_DEV too generic? eBPF atached to netdev can
>> be many kinds, such as XDP, TC, etc.
> 
> yes.
> 
>>
>> I think that use TAP_TXFILTER instaed of DEV_FILTER maybe better?
>> and TAP_FILTER->BPF_DEV. Make them similar to the name in
>> __tun_chr_ioctl() may be easier for user to understand.
>>
> 
> in this case given the unique attach points and API tap in the name
> seems more appropriate
> 

Thank you very much for the suggestions.

I will add below in the next version.

SKB_DROP_REASON_TAP_TXFILTER,	/* dropped by tx filter implemented at
				 * tun/tap, e.g., check_filter()
				 */
SKB_DROP_REASON_TAP_FILTER,	/* dropped by (ebpf) filter directly
				 * attached to tun/tap, e.g., via
				 * TUNSETFILTEREBPF
				 */

Dongli Zhang

Re: [PATCH net-next v3 0/3] tun/tap: use kfree_skb_reason() to trace dropped skb

[Dongli Zhang]

The subject should be [PATCH net-next v3 0/4] but not [PATCH net-next v3 0/3].

Sorry for the mistake.

Dongli Zhang

On 2/20/22 9:34 PM, Dongli Zhang wrote:
> The commit c504e5c2f964 ("net: skb: introduce kfree_skb_reason()") has
> introduced the kfree_skb_reason() to help track the reason.
> 
> The tun and tap are commonly used as virtio-net/vhost-net backend. This is to
> use kfree_skb_reason() to trace the dropped skb for those two drivers. 
> 
> Changed since v1:
> - I have renamed many of the reasons since v1. I make them as generic as
>   possible so that they can be re-used by core networking and drivers.
> 
> Changed since v2:
> - declare drop_reason as type "enum skb_drop_reason"
> - handle the drop in skb_list_walk_safe() case for tap driver, and
>   kfree_skb_list_reason() is introduced
> 
> 
> The following reasons are introduced.
> 
> - SKB_DROP_REASON_SKB_CSUM
> 
> This is used whenever there is checksum error with sk_buff.
> 
> - SKB_DROP_REASON_SKB_COPY_DATA
> 
> The kernel may (zero) copy the data to or from sk_buff, e.g.,
> zerocopy_sg_from_iter(), skb_copy_datagram_from_iter() and
> skb_orphan_frags_rx(). This reason is for the copy related error.
> 
> - SKB_DROP_REASON_SKB_GSO_SEG
> 
> Any error reported when GSO processing the sk_buff. It is frequent to process
> sk_buff gso data and we introduce a new reason to handle that.
> 	
> - SKB_DROP_REASON_SKB_PULL
> - SKB_DROP_REASON_SKB_TRIM
> 
> It is frequent to pull to sk_buff data or trim the sk_buff data.
> 
> - SKB_DROP_REASON_DEV_HDR
> 
> Any driver may report error if there is any error in the metadata on the DMA
> ring buffer.
> 
> - SKB_DROP_REASON_DEV_READY
> 
> The device is not ready/online or initialized to receive data.
> 
> - SKB_DROP_REASON_DEV_FILTER
> 
> David Ahern suggested SKB_DROP_REASON_TAP_FILTER. I changed from 'TAP' to 'DEV'
> to make it more generic.
> 
> - SKB_DROP_REASON_FULL_RING
> 
> Suggested by Eric Dumazet.
> 
> - SKB_DROP_REASON_BPF_FILTER
> 
> Dropped by ebpf filter
> 
> 
> This is the output for TUN device.
> 
> # cat /sys/kernel/debug/tracing/trace_pipe
>           <idle>-0       [018] ..s1.  1478.130490: kfree_skb: skbaddr=00000000c4f21b8d protocol=0 location=00000000aff342c7 reason: NOT_SPECIFIED
>       vhost-9003-9020    [012] b..1.  1478.196264: kfree_skb: skbaddr=00000000b174fb9b protocol=2054 location=000000001cf38db0 reason: FULL_RING
>           arping-9639    [018] b..1.  1479.082993: kfree_skb: skbaddr=00000000c4f21b8d protocol=2054 location=000000001cf38db0 reason: FULL_RING
>           <idle>-0       [012] b.s3.  1479.110472: kfree_skb: skbaddr=00000000e0c3681f protocol=4 location=000000001cf38db0 reason: FULL_RING
>           arping-9639    [018] b..1.  1480.083086: kfree_skb: skbaddr=00000000c4f21b8d protocol=2054 location=000000001cf38db0 reason: FULL_RING
> 
> 
> This is the output for TAP device.
> 
> # cat /sys/kernel/debug/tracing/trace_pipe
>           <idle>-0       [014] ..s1.  1096.418621: kfree_skb: skbaddr=00000000f8f41946 protocol=0 location=00000000aff342c7 reason: NOT_SPECIFIED
>           arping-7006    [001] ..s1.  1096.843961: kfree_skb: skbaddr=000000002ec803a8 protocol=2054 location=000000009a57b32f reason: FULL_RING
>           arping-7006    [001] ..s1.  1097.844035: kfree_skb: skbaddr=000000002ec803a8 protocol=2054 location=000000009a57b32f reason: FULL_RING
>           arping-7006    [001] ..s1.  1098.844102: kfree_skb: skbaddr=00000000295eb0da protocol=2054 location=000000009a57b32f reason: FULL_RING
>           arping-7006    [001] ..s1.  1099.844160: kfree_skb: skbaddr=00000000295eb0da protocol=2054 location=000000009a57b32f reason: FULL_RING
>           arping-7006    [001] ..s1.  1100.844214: kfree_skb: skbaddr=00000000295eb0da protocol=2054 location=000000009a57b32f reason: FULL_RING
>           arping-7006    [001] ..s1.  1101.844230: kfree_skb: skbaddr=00000000295eb0da protocol=2054 location=000000009a57b32f reason: FULL_RING
> 
> 
>  drivers/net/tap.c          | 35 +++++++++++++++++++++++++----------
>  drivers/net/tun.c          | 38 ++++++++++++++++++++++++++++++--------
>  include/linux/skbuff.h     | 18 ++++++++++++++++++
>  include/trace/events/skb.h | 10 ++++++++++
>  net/core/skbuff.c          | 11 +++++++++--
>  5 files changed, 92 insertions(+), 20 deletions(-)
> 
> Please let me know if there is any suggestion on the definition of reasons.
> 
> Thank you very much!
> 
> Dongli Zhang
> 
>