netdev - [PATCH] net: Reduce skb_warn_bad

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Message-Id: <1501852317-11684-1-git-send-email-xiangxia.m.yue@gmail.com>
Date:   Fri,  4 Aug 2017 06:11:57 -0700
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     netdev@...r.kernel.org
Cc:     Tonghao Zhang <xiangxia.m.yue@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Pravin B Shelar <pshelar@....org>
Subject: [PATCH] net: Reduce skb_warn_bad_offload() noise.

This patch will revert the b2504a5dbe "net: reduce
skb_warn_bad_offload() noise". The ovs will call the
__skb_gso_segment() with tx false. When segmenting UDP with UFO,
the __skb_gso_segment raises a warning as below [1], because the
ip_summed is CHECKSUM_NONE. While the net-next has removed the
UFO support, but the 4.11 and 4.12 kernel don't address that problem.

In the kernel, only qdisc_pkt_len_init() (__dev_queue_xmit call it.)
uses the SKB_GSO_DODGY to do something. Other places just set it.
The warn described in b2504a5dbe is shown [2]. We may know that:
    1. the net_device don’t have qdisc.
    2. the skb->ip_summed was changed to CHECKSUM_NONE. it maybe
    changed in skb_checksum_help() when calling validate_xmit_skb().
    or other place.

And we should not revert the  6e7bc478c9 "net: skb_needs_check() accepts
CHECKSUM_NONE for tx". The check is necessary.

[1]
[321428.168903] WARNING: CPU: 0 PID: 2279 at net/core/dev.c:2562
skb_warn_bad_offload+0xc4/0x110
[321428.168906] san0: caps=(0x000004009fbb58e9, 0x0000000000000000) len=6769
data_len=6727 gso_size=1480 gso_type=2 ip_summed=0

[321428.168955] CPU: 0 PID: 2279 Comm: ruby-mri 4.11.12-200.fc25.x86_64 #1
[321428.168956] Hardware name: Supermicro SYS-1028U-TNRTP+/X10DRU-i+, BIOS 1.1 07/22/2015
[321428.168957] Call Trace:
[321428.168962]  dump_stack+0x63/0x86
[321428.168965]  __warn+0xcb/0xf0
[321428.168966]  warn_slowpath_fmt+0x5a/0x80
[321428.168968]  skb_warn_bad_offload+0xc4/0x110
[321428.168970]  __skb_gso_segment+0x190/0x1a0
[321428.168977]  queue_gso_packets+0x62/0x160 [openvswitch]
[321428.168992]  ovs_dp_upcall+0x31/0x60 [openvswitch]
[321428.168994]  ovs_dp_process_packet+0x10d/0x130 [openvswitch]
[321428.168997]  ovs_vport_receive+0x76/0xd0 [openvswitch]
[321428.169013]  internal_dev_xmit+0x28/0x60 [openvswitch]
[321428.169014]  dev_hard_start_xmit+0xa3/0x1f0
[321428.169016]  __dev_queue_xmit+0x592/0x650
[321428.169026]  dev_queue_xmit+0x10/0x20

[2]
WARNING: CPU: 1 PID: 6768 at net/core/dev.c:2439 skb_warn_bad_offload+0x2af/0x390 net/core/dev.c:2434
lo: caps=(0x000000a2803b7c69, 0x0000000000000000) len=138 data_len=0 gso_size=15883 gso_type=4 ip_summed=0
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 6768 Comm: syz-executor1 Not tainted 4.9.0 #5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
ffff8801c063ecd8 ffffffff82346bdf ffffffff00000001 1ffff100380c7d2e
ffffed00380c7d26 0000000041b58ab3 ffffffff84b37e38 ffffffff823468f1
ffffffff84820740 ffffffff84f289c0 dffffc0000000000 ffff8801c063ee20
Call Trace:
[<ffffffff82346bdf>] __dump_stack lib/dump_stack.c:15 [inline]
[<ffffffff82346bdf>] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
[<ffffffff81827e34>] panic+0x1fb/0x412 kernel/panic.c:179
[<ffffffff8141f704>] __warn+0x1c4/0x1e0 kernel/panic.c:542
[<ffffffff8141f7e5>] warn_slowpath_fmt+0xc5/0x100 kernel/panic.c:565
[<ffffffff8356cbaf>] skb_warn_bad_offload+0x2af/0x390 net/core/dev.c:2434
[<ffffffff83585cd2>] __skb_gso_segment+0x482/0x780 net/core/dev.c:2706
[<ffffffff83586f19>] skb_gso_segment include/linux/netdevice.h:3985 [inline]
[<ffffffff83586f19>] validate_xmit_skb+0x5c9/0xc20 net/core/dev.c:2969
[<ffffffff835892bb>] __dev_queue_xmit+0xe6b/0x1e70 net/core/dev.c:3383
[<ffffffff8358a2d7>] dev_queue_xmit+0x17/0x20 net/core/dev.c:3424

Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Willem de Bruijn <willemb@...gle.com>
Cc: Pravin B Shelar <pshelar@....org>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
---
 net/core/dev.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 1d75499..97e6989 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2753,11 +2753,11 @@ static inline bool skb_needs_check(struct sk_buff *skb, bool tx_path)
 struct sk_buff *__skb_gso_segment(struct sk_buff *skb,
 				  netdev_features_t features, bool tx_path)
 {
-	struct sk_buff *segs;
-
 	if (unlikely(skb_needs_check(skb, tx_path))) {
 		int err;
 
+		skb_warn_bad_offload(skb);
+
 		/* We're going to init ->check field in TCP or UDP header */
 		err = skb_cow_head(skb, 0);
 		if (err < 0)
@@ -2786,12 +2786,7 @@ struct sk_buff *__skb_gso_segment(struct sk_buff *skb,
 	skb_reset_mac_header(skb);
 	skb_reset_mac_len(skb);
 
-	segs = skb_mac_gso_segment(skb, features);
-
-	if (unlikely(skb_needs_check(skb, tx_path)))
-		skb_warn_bad_offload(skb);
-
-	return segs;
+	return skb_mac_gso_segment(skb, features);
 }
 EXPORT_SYMBOL(__skb_gso_segment);
 
-- 
1.8.3.1