Re: [syzbot] [ppp?] inconsistent lock state in valid_state (4)

syzbot has found a reproducer for the following issue on:

HEAD commit:    b311c1b497e5 Merge tag '6.11-rc4-server-fixes' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12dccc7b980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=df2f0ed7e30a639d
dashboard link: https://syzkaller.appspot.com/bug?extid=d43eb079c2addf2439c3
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17cf93d5980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=101bb693980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-b311c1b4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1c99fa48192f/vmlinux-b311c1b4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/16d5710a012a/bzImage-b311c1b4.xz

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

================================
WARNING: inconsistent lock state
6.11.0-rc4-syzkaller-00019-gb311c1b497e5 #0 Not tainted
--------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
ksoftirqd/0/16 [HC0[0]:SC1[1]:HE1:SE0] takes:
ffff888039c531e0 (&pch->downl){+.?.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff888039c531e0 (&pch->downl){+.?.}-{2:2}, at: ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2272 [inline]
ffff888039c531e0 (&pch->downl){+.?.}-{2:2}, at: ppp_input+0x18b/0xa10 drivers/net/ppp/ppp_generic.c:2304
{SOFTIRQ-ON-W} state was registered at:
  lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
  __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+0x18b/0xa10 drivers/net/ppp/ppp_generic.c:2304
  pppoe_rcv_core+0x117/0x310 drivers/net/ppp/pppoe.c:379
  sk_backlog_rcv include/net/sock.h:1111 [inline]
  __release_sock+0x243/0x350 net/core/sock.c:3004
  release_sock+0x61/0x1f0 net/core/sock.c:3558
  pppoe_sendmsg+0xd5/0x750 drivers/net/ppp/pppoe.c:903
  sock_sendmsg_nosec net/socket.c:730 [inline]
  __sock_sendmsg+0x221/0x270 net/socket.c:745
  ____sys_sendmsg+0x525/0x7d0 net/socket.c:2597
  ___sys_sendmsg net/socket.c:2651 [inline]
  __sys_sendmmsg+0x3b2/0x740 net/socket.c:2737
  __do_sys_sendmmsg net/socket.c:2766 [inline]
  __se_sys_sendmmsg net/socket.c:2763 [inline]
  __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2763
  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
  entry_SYSCALL_64_after_hwframe+0x77/0x7f
irq event stamp: 1309336
hardirqs last  enabled at (1309336): [<ffffffff8bc0d5ff>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:151 [inline]
hardirqs last  enabled at (1309336): [<ffffffff8bc0d5ff>] _raw_spin_unlock_irqrestore+0x8f/0x140 kernel/locking/spinlock.c:194
hardirqs last disabled at (1309335): [<ffffffff8bc0d300>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (1309335): [<ffffffff8bc0d300>] _raw_spin_lock_irqsave+0xb0/0x120 kernel/locking/spinlock.c:162
softirqs last  enabled at (1309326): [<ffffffff81578ffa>] run_ksoftirqd+0xca/0x130 kernel/softirq.c:928
softirqs last disabled at (1309331): [<ffffffff81578ffa>] run_ksoftirqd+0xca/0x130 kernel/softirq.c:928

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: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:326 [inline]
 #0: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #0: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2267 [inline]
 #0: ffffffff8e938320 (rcu_read_lock){....}-{1:2}, at: ppp_input+0x55/0xa10 drivers/net/ppp/ppp_generic.c:2304

stack backtrace:
CPU: 0 UID: 0 PID: 16 Comm: ksoftirqd/0 Not tainted 6.11.0-rc4-syzkaller-00019-gb311c1b497e5 #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+0x241/0x360 lib/dump_stack.c:119
 valid_state+0x13a/0x1c0 kernel/locking/lockdep.c:4012
 mark_lock_irq+0xbb/0xc20 kernel/locking/lockdep.c:4215
 mark_lock+0x223/0x350 kernel/locking/lockdep.c:4677
 __lock_acquire+0xbf9/0x2040 kernel/locking/lockdep.c:5096
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
 __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+0x18b/0xa10 drivers/net/ppp/ppp_generic.c:2304
 ppp_sync_process+0x71/0x160 drivers/net/ppp/ppp_synctty.c:490
 tasklet_action_common+0x321/0x4d0 kernel/softirq.c:785
 handle_softirqs+0x2c4/0x970 kernel/softirq.c:554
 run_ksoftirqd+0xca/0x130 kernel/softirq.c:928
 smpboot_thread_fn+0x544/0xa30 kernel/smpboot.c:164
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>


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