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

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in __dev_queue_xmit

============================================
WARNING: possible recursive locking detected
6.7.0-rc2-syzkaller-00195-g0f5cc96c367f-dirty #0 Not tainted
--------------------------------------------
syz-executor.0/5352 is trying to acquire lock:
ffff88806adeb8d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88806adeb8d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4403 [inline]
ffff88806adeb8d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x1622/0x38e0 net/core/dev.c:4344

but task is already holding lock:
ffff8880762430d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff8880762430d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4403 [inline]
ffff8880762430d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: sch_direct_xmit+0x1c4/0x5f0 net/sched/sch_generic.c:340

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

       CPU0
       ----
  lock(&queue->_xmit_lock);
  lock(&queue->_xmit_lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

6 locks held by syz-executor.0/5352:
 #0: ffffffff8cb25ba0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:301 [inline]
 #0: ffffffff8cb25ba0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]
 #0: ffffffff8cb25ba0 (rcu_read_lock){....}-{1:2}, at: ip_finish_output2+0x467/0x1360 net/ipv4/ip_output.c:228
 #1: ffffffff8cb25c00 (rcu_read_lock_bh){....}-{1:2}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #1: ffffffff8cb25c00 (rcu_read_lock_bh){....}-{1:2}, at: rcu_read_lock_bh include/linux/rcupdate.h:799 [inline]
 #1: ffffffff8cb25c00 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x23e/0x38e0 net/core/dev.c:4273
 #2: ffff88807f8e0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: spin_trylock include/linux/spinlock.h:361 [inline]
 #2: ffff88807f8e0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:194 [inline]
 #2: ffff88807f8e0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3761 [inline]
 #2: ffff88807f8e0258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_queue_xmit+0x11d0/0x38e0 net/core/dev.c:4314
 #3: ffff8880762430d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #3: ffff8880762430d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4403 [inline]
 #3: ffff8880762430d8 (&queue->_xmit_lock){+.-.}-{2:2}, at: sch_direct_xmit+0x1c4/0x5f0 net/sched/sch_generic.c:340
 #4: ffffffff8cb25ba0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:301 [inline]
 #4: ffffffff8cb25ba0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]
 #4: ffffffff8cb25ba0 (rcu_read_lock){....}-{1:2}, at: ip_finish_output2+0x467/0x1360 net/ipv4/ip_output.c:228
 #5: ffffffff8cb25c00 (rcu_read_lock_bh){....}-{1:2}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
 #5: ffffffff8cb25c00 (rcu_read_lock_bh){....}-{1:2}, at: rcu_read_lock_bh include/linux/rcupdate.h:799 [inline]
 #5: ffffffff8cb25c00 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x23e/0x38e0 net/core/dev.c:4273

stack backtrace:
CPU: 1 PID: 5352 Comm: syz-executor.0 Not tainted 6.7.0-rc2-syzkaller-00195-g0f5cc96c367f-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 __lock_acquire+0x6a81/0x7f70 kernel/locking/lockdep.c:3062
 lock_acquire+0x1e3/0x520 kernel/locking/lockdep.c:5753
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 __netif_tx_lock include/linux/netdevice.h:4403 [inline]
 __dev_queue_xmit+0x1622/0x38e0 net/core/dev.c:4344
 ip_finish_output2+0xe6d/0x1360 include/net/neighbour.h:542
 iptunnel_xmit+0x540/0x9b0 net/ipv4/ip_tunnel_core.c:82
 ip_tunnel_xmit+0x20e4/0x2940 net/ipv4/ip_tunnel.c:831
 erspan_xmit+0x9c6/0x13e0 net/ipv4/ip_gre.c:717
 __netdev_start_xmit include/linux/netdevice.h:4940 [inline]
 netdev_start_xmit include/linux/netdevice.h:4954 [inline]
 xmit_one net/core/dev.c:3547 [inline]
 dev_hard_start_xmit+0x241/0x750 net/core/dev.c:3563
 sch_direct_xmit+0x2b6/0x5f0 net/sched/sch_generic.c:342
 __dev_queue_xmit+0x187c/0x38e0 net/core/dev.c:3774
 ip_finish_output2+0xe6d/0x1360 include/net/neighbour.h:542
 ip_send_skb+0x117/0x1b0 include/net/dst.h:451
 udp_send_skb+0x931/0x1200 net/ipv4/udp.c:963
 udp_sendmsg+0x1c17/0x2a70 net/ipv4/udp.c:1250
 udpv6_sendmsg+0x1342/0x3220 net/ipv6/udp.c:1390
 ____sys_sendmsg+0x592/0x890 net/socket.c:730
 __sys_sendmmsg+0x3b2/0x730 net/socket.c:2638
 __do_sys_sendmmsg net/socket.c:2753 [inline]
 __se_sys_sendmmsg net/socket.c:2750 [inline]
 __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2750
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f25aa8798a9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f25a9ffe0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f25aa98bf60 RCX: 00007f25aa8798a9
RDX: 0000000000000001 RSI: 0000000020004d80 RDI: 0000000000000004
RBP: 00007f25aa8d5074 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000004000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f25aa98bf60 R15: 00007fff36da4898
 </TASK>


Tested on:

commit:         0f5cc96c Merge tag 's390-6.7-3' of git://git.kernel.or..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=117ea4d8e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3813bb4934ffb745
dashboard link: https://syzkaller.appspot.com/bug?extid=e18ac85757292b7baf96
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=139c7daf680000