Subject: Re: [syzbot] possible deadlock in sch_direct_xmit (2)

From: syzbot <[email-masked]>
Date: Thu, 28 Oct 2021 19:08:21 -0700

syzbot has found a reproducer for the following issue on:

HEAD commit:    35392da51b1a Revert "net: hns3: fix pause config problem a..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=108cede2b00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ca74db36f5f0f1c4
dashboard link: https://syzkaller.appspot.com/bug?extid=e18ac85757292b7baf96
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15d2f204b00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=112f3f6cb00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

============================================
WARNING: possible recursive locking detected
5.15.0-rc6-syzkaller #0 Not tainted
--------------------------------------------
syz-executor023/6539 is trying to acquire lock:
ffff88801c693398 (_xmit_ETHER#2){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
ffff88801c693398 (_xmit_ETHER#2){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4405 [inline]
ffff88801c693398 (_xmit_ETHER#2){+.-.}-{2:2}, at: sch_direct_xmit+0x30f/0xbc0 net/sched/sch_generic.c:340

but task is already holding lock:
ffff88801d04fc98 (_xmit_ETHER#2){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
ffff88801d04fc98 (_xmit_ETHER#2){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4405 [inline]
ffff88801d04fc98 (_xmit_ETHER#2){+.-.}-{2:2}, at: sch_direct_xmit+0x30f/0xbc0 net/sched/sch_generic.c:340

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(_xmit_ETHER#2);
  lock(_xmit_ETHER#2);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

7 locks held by syz-executor023/6539:
 #0: ffffffff8b981ac0 (rcu_read_lock_bh){....}-{1:2}, at: lwtunnel_xmit_redirect include/net/lwtunnel.h:95 [inline]
 #0: ffffffff8b981ac0 (rcu_read_lock_bh){....}-{1:2}, at: ip_finish_output2+0x28b/0x2140 net/ipv4/ip_output.c:207
 #1: ffffffff8b981ac0 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x1d5/0x36e0 net/core/dev.c:4143
 #2: ffff88801a4f5258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: spin_trylock include/linux/spinlock.h:373 [inline]
 #2: ffff88801a4f5258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:173 [inline]
 #2: ffff88801a4f5258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3796 [inline]
 #2: ffff88801a4f5258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_queue_xmit+0x1222/0x36e0 net/core/dev.c:4177
 #3: ffff88801d04fc98 (_xmit_ETHER#2){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #3: ffff88801d04fc98 (_xmit_ETHER#2){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4405 [inline]
 #3: ffff88801d04fc98 (_xmit_ETHER#2){+.-.}-{2:2}, at: sch_direct_xmit+0x30f/0xbc0 net/sched/sch_generic.c:340
 #4: ffffffff8b981ac0 (rcu_read_lock_bh){....}-{1:2}, at: lwtunnel_xmit_redirect include/net/lwtunnel.h:95 [inline]
 #4: ffffffff8b981ac0 (rcu_read_lock_bh){....}-{1:2}, at: ip_finish_output2+0x28b/0x2140 net/ipv4/ip_output.c:207
 #5: ffffffff8b981ac0 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x1d5/0x36e0 net/core/dev.c:4143
 #6: ffff88807762e258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: spin_trylock include/linux/spinlock.h:373 [inline]
 #6: ffff88807762e258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:173 [inline]
 #6: ffff88807762e258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3796 [inline]
 #6: ffff88807762e258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_queue_xmit+0x1222/0x36e0 net/core/dev.c:4177

stack backtrace:
CPU: 0 PID: 6539 Comm: syz-executor023 Not tainted 5.15.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2944 [inline]
 check_deadlock kernel/locking/lockdep.c:2987 [inline]
 validate_chain kernel/locking/lockdep.c:3776 [inline]
 __lock_acquire.cold+0x149/0x3ab kernel/locking/lockdep.c:5015
 lock_acquire kernel/locking/lockdep.c:5625 [inline]
 lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
 __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
 _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:363 [inline]
 __netif_tx_lock include/linux/netdevice.h:4405 [inline]
 sch_direct_xmit+0x30f/0xbc0 net/sched/sch_generic.c:340
 __dev_xmit_skb net/core/dev.c:3809 [inline]
 __dev_queue_xmit+0x1489/0x36e0 net/core/dev.c:4177
 neigh_resolve_output net/core/neighbour.c:1492 [inline]
 neigh_resolve_output+0x50e/0x820 net/core/neighbour.c:1472
 neigh_output include/net/neighbour.h:510 [inline]
 ip_finish_output2+0x813/0x2140 net/ipv4/ip_output.c:221
 __ip_finish_output net/ipv4/ip_output.c:299 [inline]
 __ip_finish_output+0x396/0x640 net/ipv4/ip_output.c:281
 ip_finish_output+0x32/0x200 net/ipv4/ip_output.c:309
 NF_HOOK_COND include/linux/netfilter.h:296 [inline]
 ip_output+0x196/0x310 net/ipv4/ip_output.c:423
 dst_output include/net/dst.h:450 [inline]
 ip_local_out+0xaf/0x1a0 net/ipv4/ip_output.c:126
 iptunnel_xmit+0x628/0xa50 net/ipv4/ip_tunnel_core.c:82
 ip_tunnel_xmit+0x10a6/0x2b60 net/ipv4/ip_tunnel.c:810
 erspan_xmit+0x7e2/0x29c0 net/ipv4/ip_gre.c:712
 __netdev_start_xmit include/linux/netdevice.h:4988 [inline]
 netdev_start_xmit include/linux/netdevice.h:5002 [inline]
 xmit_one net/core/dev.c:3582 [inline]
 dev_hard_start_xmit+0x1eb/0x920 net/core/dev.c:3598
 sch_direct_xmit+0x19f/0xbc0 net/sched/sch_generic.c:342
 __dev_xmit_skb net/core/dev.c:3809 [inline]
 __dev_queue_xmit+0x1489/0x36e0 net/core/dev.c:4177
 neigh_resolve_output net/core/neighbour.c:1492 [inline]
 neigh_resolve_output+0x50e/0x820 net/core/neighbour.c:1472
 neigh_output include/net/neighbour.h:510 [inline]
 ip_finish_output2+0x813/0x2140 net/ipv4/ip_output.c:221
 __ip_finish_output net/ipv4/ip_output.c:299 [inline]
 __ip_finish_output+0x396/0x640 net/ipv4/ip_output.c:281
 ip_finish_output+0x32/0x200 net/ipv4/ip_output.c:309
 NF_HOOK_COND include/linux/netfilter.h:296 [inline]
 ip_output+0x196/0x310 net/ipv4/ip_output.c:423
 dst_output include/net/dst.h:450 [inline]
 ip_local_out net/ipv4/ip_output.c:126 [inline]
 ip_send_skb+0xd4/0x260 net/ipv4/ip_output.c:1555
 udp_send_skb+0x6cd/0x11a0 net/ipv4/udp.c:967
 udp_sendmsg+0x1bad/0x2740 net/ipv4/udp.c:1254
 udpv6_sendmsg+0x14f6/0x2c40 net/ipv6/udp.c:1360
 inet6_sendmsg+0x99/0xe0 net/ipv6/af_inet6.c:643
 sock_sendmsg_nosec net/socket.c:704 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:724
 ____sys_sendmsg+0x331/0x810 net/socket.c:2409
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2463
 __sys_sendmmsg+0x195/0x470 net/socket.c:2549
 __do_sys_sendmmsg net/socket.c:2578 [inline]
 __se_sys_sendmmsg net/socket.c:2575 [inline]
 __x64_sys_sendmmsg+0x99/0x100 net/socket.c:2575
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f728d0d9aa9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffda2643b88 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f728d0d9aa9
RDX: 0000000000000001 RSI: 0000000020004d8