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Date:   Wed, 7 Oct 2020 08:26:28 +0800
From:   kernel test robot <lkp@...el.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, bpf@...r.kernel.org
Cc:     kbuild-all@...ts.01.org, clang-built-linux@...glegroups.com,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        netdev@...r.kernel.org, Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        maze@...gle.com, lmb@...udflare.com, shaun@...era.io,
        Lorenzo Bianconi <lorenzo@...nel.org>, marek@...udflare.com
Subject: Re: [PATCH bpf-next V1 5/6] bpf: Add MTU check for TC-BPF packets
 after egress hook

Hi Jesper,

I love your patch! Perhaps something to improve:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/0day-ci/linux/commits/Jesper-Dangaard-Brouer/bpf-New-approach-for-BPF-MTU-handling-and-enforcement/20201007-000903
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: mips-randconfig-r024-20201005 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 1127662c6dc2a276839c75a42238b11a3ad00f32)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install mips cross compiling tool for clang build
        # apt-get install binutils-mips-linux-gnu
        # https://github.com/0day-ci/linux/commit/2065cee7d6b74c8f1dabae4e4e15999a841e3349
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Jesper-Dangaard-Brouer/bpf-New-approach-for-BPF-MTU-handling-and-enforcement/20201007-000903
        git checkout 2065cee7d6b74c8f1dabae4e4e15999a841e3349
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=mips 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@...el.com>

All warnings (new ones prefixed by >>):

   net/core/dev.c:4176:1: warning: unused label 'drop'
   drop:
   ^~~~~
>> net/core/dev.c:4068:7: warning: unused variable 'mtu_check'
   bool mtu_check = false;
   ^
   net/core/dev.c:4949:1: warning: unused function 'sch_handle_ingress'
   sch_handle_ingress(struct sk_buff struct packet_type int
   ^
   net/core/dev.c:5094:19: warning: unused function 'nf_ingress'
   static inline int nf_ingress(struct sk_buff struct packet_type
   ^
   fatal error: error in backend: Nested variants found in inline asm string: ' .set push
   .set noat
   .set push
   .set arch=r4000
   .if ( 0x00 ) != -1)) 0x00 ) != -1)) : ($( static struct ftrace_branch_data __attribute__((__aligned__(4))) __attribute__((__section__("_ftrace_branch"))) __if_trace = $( .func = __func__, .file = "arch/mips/include/asm/cmpxchg.h", .line = 163, $); 0x00 ) != -1)) : $))) ) && ( 0 ); .set push; .set mips64r2; .rept 1; sync 0x00; .endr; .set pop; .else; ; .endif
   1: ll $0, $2 # __cmpxchg_asm
   bne $0, ${3:z}, 2f
   .set pop
   move $$1, ${4:z}
   .set arch=r4000
   sc $$1, $1
   beqz $$1, 1b
   .set pop
   2: .if ( 0x00 ) != -1)) 0x00 ) != -1)) : ($( static struct ftrace_branch_data __attribute__((__aligned__(4))) __attribute__((__section__("_ftrace_branch"))) __if_trace = $( .func = __func__, .file = "arch/mips/include/asm/cmpxchg.h", .line = 163, $); 0x00 ) != -1)) : $))) ) && ( 0 ); .set push; .set mips64r2; .rept 1; sync 0x00; .endr; .set pop; .else; ; .endif
   '
   clang-12: error: clang frontend command failed with exit code 70 (use -v to see invocation)
   clang version 12.0.0 (git://gitmirror/llvm_project 1127662c6dc2a276839c75a42238b11a3ad00f32)
   Target: mipsel-unknown-linux-gnu
   Thread model: posix
   InstalledDir: /opt/cross/clang-1127662c6d/bin
   clang-12: note: diagnostic msg:
   Makefile arch drivers include kernel net scripts source usr
--
>> net/core/dev.c:4068:7: warning: unused variable 'mtu_check'
   bool mtu_check = false;
   ^
   net/core/dev.c:4176:1: warning: unused label 'drop'
   drop:
   ^~~~~
   net/core/dev.c:4949:1: warning: unused function 'sch_handle_ingress'
   sch_handle_ingress(struct sk_buff struct packet_type int
   ^
   net/core/dev.c:5094:19: warning: unused function 'nf_ingress'
   static inline int nf_ingress(struct sk_buff struct packet_type
   ^
   fatal error: error in backend: Nested variants found in inline asm string: ' .set push
   .set noat
   .set push
   .set arch=r4000
   .if ( 0x00 ) != -1)) 0x00 ) != -1)) : ($( static struct ftrace_branch_data __attribute__((__aligned__(4))) __attribute__((__section__("_ftrace_branch"))) __if_trace = $( .func = __func__, .file = "arch/mips/include/asm/cmpxchg.h", .line = 163, $); 0x00 ) != -1)) : $))) ) && ( 0 ); .set push; .set mips64r2; .rept 1; sync 0x00; .endr; .set pop; .else; ; .endif
   1: ll $0, $2 # __cmpxchg_asm
   bne $0, ${3:z}, 2f
   .set pop
   move $$1, ${4:z}
   .set arch=r4000
   sc $$1, $1
   beqz $$1, 1b
   .set pop
   2: .if ( 0x00 ) != -1)) 0x00 ) != -1)) : ($( static struct ftrace_branch_data __attribute__((__aligned__(4))) __attribute__((__section__("_ftrace_branch"))) __if_trace = $( .func = __func__, .file = "arch/mips/include/asm/cmpxchg.h", .line = 163, $); 0x00 ) != -1)) : $))) ) && ( 0 ); .set push; .set mips64r2; .rept 1; sync 0x00; .endr; .set pop; .else; ; .endif
   '
   clang-12: error: clang frontend command failed with exit code 70 (use -v to see invocation)
   clang version 12.0.0 (git://gitmirror/llvm_project 1127662c6dc2a276839c75a42238b11a3ad00f32)
   Target: mipsel-unknown-linux-gnu
   Thread model: posix
   InstalledDir: /opt/cross/clang-1127662c6d/bin
   clang-12: note: diagnostic msg:
   Makefile arch drivers include kernel net scripts source usr

vim +/mtu_check +4068 net/core/dev.c

  4037	
  4038	/**
  4039	 *	__dev_queue_xmit - transmit a buffer
  4040	 *	@skb: buffer to transmit
  4041	 *	@sb_dev: suboordinate device used for L2 forwarding offload
  4042	 *
  4043	 *	Queue a buffer for transmission to a network device. The caller must
  4044	 *	have set the device and priority and built the buffer before calling
  4045	 *	this function. The function can be called from an interrupt.
  4046	 *
  4047	 *	A negative errno code is returned on a failure. A success does not
  4048	 *	guarantee the frame will be transmitted as it may be dropped due
  4049	 *	to congestion or traffic shaping.
  4050	 *
  4051	 * -----------------------------------------------------------------------------------
  4052	 *      I notice this method can also return errors from the queue disciplines,
  4053	 *      including NET_XMIT_DROP, which is a positive value.  So, errors can also
  4054	 *      be positive.
  4055	 *
  4056	 *      Regardless of the return value, the skb is consumed, so it is currently
  4057	 *      difficult to retry a send to this method.  (You can bump the ref count
  4058	 *      before sending to hold a reference for retry if you are careful.)
  4059	 *
  4060	 *      When calling this method, interrupts MUST be enabled.  This is because
  4061	 *      the BH enable code must have IRQs enabled so that it will not deadlock.
  4062	 *          --BLG
  4063	 */
  4064	static int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
  4065	{
  4066		struct net_device *dev = skb->dev;
  4067		struct netdev_queue *txq;
> 4068		bool mtu_check = false;
  4069		bool again = false;
  4070		struct Qdisc *q;
  4071		int rc = -ENOMEM;
  4072	
  4073		skb_reset_mac_header(skb);
  4074	
  4075		if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP))
  4076			__skb_tstamp_tx(skb, NULL, skb->sk, SCM_TSTAMP_SCHED);
  4077	
  4078		/* Disable soft irqs for various locks below. Also
  4079		 * stops preemption for RCU.
  4080		 */
  4081		rcu_read_lock_bh();
  4082	
  4083		skb_update_prio(skb);
  4084	
  4085		qdisc_pkt_len_init(skb);
  4086	#ifdef CONFIG_NET_CLS_ACT
  4087		mtu_check = skb_is_redirected(skb);
  4088		skb->tc_at_ingress = 0;
  4089	# ifdef CONFIG_NET_EGRESS
  4090		if (static_branch_unlikely(&egress_needed_key)) {
  4091			unsigned int len_orig = skb->len;
  4092	
  4093			skb = sch_handle_egress(skb, &rc, dev);
  4094			if (!skb)
  4095				goto out;
  4096			/* BPF-prog ran and could have changed packet size beyond MTU */
  4097			if (rc == NET_XMIT_SUCCESS && skb->len > len_orig)
  4098				mtu_check = true;
  4099		}
  4100	# endif
  4101		/* MTU-check only happens on "last" net_device in a redirect sequence
  4102		 * (e.g. above sch_handle_egress can steal SKB and skb_do_redirect it
  4103		 * either ingress or egress to another device).
  4104		 */
  4105		if (mtu_check && !is_skb_forwardable(dev, skb)) {
  4106			rc = -EMSGSIZE;
  4107			goto drop;
  4108		}
  4109	#endif
  4110		/* If device/qdisc don't need skb->dst, release it right now while
  4111		 * its hot in this cpu cache.
  4112		 */
  4113		if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
  4114			skb_dst_drop(skb);
  4115		else
  4116			skb_dst_force(skb);
  4117	
  4118		txq = netdev_core_pick_tx(dev, skb, sb_dev);
  4119		q = rcu_dereference_bh(txq->qdisc);
  4120	
  4121		trace_net_dev_queue(skb);
  4122		if (q->enqueue) {
  4123			rc = __dev_xmit_skb(skb, q, dev, txq);
  4124			goto out;
  4125		}
  4126	
  4127		/* The device has no queue. Common case for software devices:
  4128		 * loopback, all the sorts of tunnels...
  4129	
  4130		 * Really, it is unlikely that netif_tx_lock protection is necessary
  4131		 * here.  (f.e. loopback and IP tunnels are clean ignoring statistics
  4132		 * counters.)
  4133		 * However, it is possible, that they rely on protection
  4134		 * made by us here.
  4135	
  4136		 * Check this and shot the lock. It is not prone from deadlocks.
  4137		 *Either shot noqueue qdisc, it is even simpler 8)
  4138		 */
  4139		if (dev->flags & IFF_UP) {
  4140			int cpu = smp_processor_id(); /* ok because BHs are off */
  4141	
  4142			if (txq->xmit_lock_owner != cpu) {
  4143				if (dev_xmit_recursion())
  4144					goto recursion_alert;
  4145	
  4146				skb = validate_xmit_skb(skb, dev, &again);
  4147				if (!skb)
  4148					goto out;
  4149	
  4150				HARD_TX_LOCK(dev, txq, cpu);
  4151	
  4152				if (!netif_xmit_stopped(txq)) {
  4153					dev_xmit_recursion_inc();
  4154					skb = dev_hard_start_xmit(skb, dev, txq, &rc);
  4155					dev_xmit_recursion_dec();
  4156					if (dev_xmit_complete(rc)) {
  4157						HARD_TX_UNLOCK(dev, txq);
  4158						goto out;
  4159					}
  4160				}
  4161				HARD_TX_UNLOCK(dev, txq);
  4162				net_crit_ratelimited("Virtual device %s asks to queue packet!\n",
  4163						     dev->name);
  4164			} else {
  4165				/* Recursion is detected! It is possible,
  4166				 * unfortunately
  4167				 */
  4168	recursion_alert:
  4169				net_crit_ratelimited("Dead loop on virtual device %s, fix it urgently!\n",
  4170						     dev->name);
  4171			}
  4172		}
  4173	
  4174		rc = -ENETDOWN;
  4175		rcu_read_unlock_bh();
  4176	drop:
  4177		atomic_long_inc(&dev->tx_dropped);
  4178		kfree_skb_list(skb);
  4179		return rc;
  4180	out:
  4181		rcu_read_unlock_bh();
  4182		return rc;
  4183	}
  4184	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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