================================
WARNING: inconsistent lock state
6.11.0-syzkaller-08068-g1ec6d097897a #0 Not tainted
--------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
ksoftirqd/0/16 [HC0[0]:SC1[1]:HE1:SE0] takes:
ffff8880498799e0 (&pch->downl){+.?.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff8880498799e0 (&pch->downl){+.?.}-{2:2}, at: ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2272 [inline]
ffff8880498799e0 (&pch->downl){+.?.}-{2:2}, at: ppp_input+0x104/0xbb0 drivers/net/ppp/ppp_generic.c:2304
{SOFTIRQ-ON-W} state was registered at:
  lock_acquire kernel/locking/lockdep.c:5822 [inline]
  lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5787
  __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]
  ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2272 [inline]
  ppp_input+0x104/0xbb0 drivers/net/ppp/ppp_generic.c:2304
  pppoe_rcv_core+0x22c/0x320 drivers/net/ppp/pppoe.c:379
  sk_backlog_rcv include/net/sock.h:1113 [inline]
  __release_sock+0x35f/0x400 net/core/sock.c:3072
  release_sock+0x5a/0x220 net/core/sock.c:3626
  pppoe_sendmsg+0x5e6/0x770 drivers/net/ppp/pppoe.c:903
  sock_sendmsg_nosec net/socket.c:730 [inline]
  __sock_sendmsg net/socket.c:745 [inline]
  ____sys_sendmsg+0xaaf/0xc90 net/socket.c:2603
  ___sys_sendmsg+0x135/0x1e0 net/socket.c:2657
  __sys_sendmmsg+0x1a1/0x450 net/socket.c:2743
  __do_sys_sendmmsg net/socket.c:2772 [inline]
  __se_sys_sendmmsg net/socket.c:2769 [inline]
  __x64_sys_sendmmsg+0x9c/0x100 net/socket.c:2769
  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
  entry_SYSCALL_64_after_hwframe+0x77/0x7f
irq event stamp: 651858
hardirqs last  enabled at (651858): [<ffffffff815008d4>] __local_bh_enable_ip+0xa4/0x120 kernel/softirq.c:387
hardirqs last disabled at (651857): [<ffffffff815008fd>] __local_bh_enable_ip+0xcd/0x120 kernel/softirq.c:364
softirqs last  enabled at (651844): [<ffffffff814ffdfb>] softirq_handle_end kernel/softirq.c:400 [inline]
softirqs last  enabled at (651844): [<ffffffff814ffdfb>] handle_softirqs+0x5bb/0x8f0 kernel/softirq.c:582
softirqs last disabled at (651849): [<ffffffff8150017a>] run_ksoftirqd kernel/softirq.c:927 [inline]
softirqs last disabled at (651849): [<ffffffff8150017a>] run_ksoftirqd+0x3a/0x60 kernel/softirq.c:919

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

       CPU0
       ----
  lock(&pch->downl);
  <Interrupt>
    lock(&pch->downl
);

 *** DEADLOCK ***

1 lock held by ksoftirqd/0/16:
 #0: ffffffff8e1b80c0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #0: ffffffff8e1b80c0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #0: ffffffff8e1b80c0 (rcu_read_lock){....}-{1:2}, at: ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2267 [inline]
 #0: ffffffff8e1b80c0 (rcu_read_lock){....}-{1:2}, at: ppp_input+0x70/0xbb0 drivers/net/ppp/ppp_generic.c:2304

stack backtrace:
CPU: 0 UID: 0 PID: 16 Comm: ksoftirqd/0 Not tainted 6.11.0-syzkaller-08068-g1ec6d097897a #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:93 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:119
 print_usage_bug.part.0+0x3a2/0x560 kernel/locking/lockdep.c:4035
 print_usage_bug kernel/locking/lockdep.c:4003 [inline]
 valid_state kernel/locking/lockdep.c:4049 [inline]
 mark_lock_irq kernel/locking/lockdep.c:4260 [inline]
 mark_lock+0x92d/0xc60 kernel/locking/lockdep.c:4722
 mark_usage kernel/locking/lockdep.c:4611 [inline]
 __lock_acquire+0x11e1/0x3ce0 kernel/locking/lockdep.c:5153
 lock_acquire kernel/locking/lockdep.c:5822 [inline]
 lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5787
 __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]
 ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2272 [inline]
 ppp_input+0x104/0xbb0 drivers/net/ppp/ppp_generic.c:2304
 ppp_async_process+0x37/0x150 drivers/net/ppp/ppp_async.c:495
 tasklet_action_common+0x24c/0x3e0 kernel/softirq.c:784
 handle_softirqs+0x213/0x8f0 kernel/softirq.c:554
 run_ksoftirqd kernel/softirq.c:927 [inline]
 run_ksoftirqd+0x3a/0x60 kernel/softirq.c:919
 smpboot_thread_fn+0x661/0xa10 kernel/smpboot.c:164
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>