WARNING: locking bug in flush_workqueue_prep_pwqs

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: cb5b020a8d38 Revert "exec: load_script: don't blindly trun..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1016c0f3400000
kernel config: https://syzkaller.appspot.com/x/.config?x=ee434566c893c7b1
dashboard link: https://syzkaller.appspot.com/bug?extid=0c4264acb66ea0484d11
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0c4264...@syzkaller.appspotmail.com

Enabled bearer <udp:syz1>, priority 10
Enabling of bearer <udp:syz1> rejected, already enabled
------------[ cut here ]------------
kobject: 'loop0' (0000000099a84316): kobject_uevent_env
DEBUG_LOCKS_WARN_ON(class_idx > MAX_LOCKDEP_KEYS)
WARNING: CPU: 0 PID: 23993 at kernel/locking/lockdep.c:3315
__lock_acquire+0x13bf/0x4700 kernel/locking/lockdep.c:3315
kobject: 'loop0' (0000000099a84316): fill_kobj_path: path
= '/devices/virtual/block/loop0'
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 23993 Comm: syz-executor.5 Not tainted 5.0.0-rc6+ #72
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
kobject: 'loop4' (00000000ed7cfd88): kobject_uevent_env
panic+0x2cb/0x65c kernel/panic.c:214
kobject: 'loop4' (00000000ed7cfd88): fill_kobj_path: path
= '/devices/virtual/block/loop4'
__warn.cold+0x20/0x45 kernel/panic.c:571
report_bug+0x263/0x2b0 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:178 [inline]
fixup_bug arch/x86/kernel/traps.c:173 [inline]
do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:__lock_acquire+0x13bf/0x4700 kernel/locking/lockdep.c:3315
Code: 8b 1d 69 a5 05 08 45 85 db 0f 85 d6 f4 ff ff 48 c7 c6 e0 a3 6b 87 48
c7 c7 40 78 6b 87 44 89 9c 24 98 00 00 00 e8 df 29 ec ff <0f> 0b 44 8b 9c
24 98 00 00 00 e9 af f4 ff ff 8b 3d dc 67 fe 08 85
RSP: 0018:ffff88806836f900 EFLAGS: 00010082
RAX: 0000000000000000 RBX: 00000000339133e8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815a9266 RDI: ffffed100d06df12
RBP: ffff88806836fac8 R08: ffff88808d184100 R09: fffffbfff1133341
R10: fffffbfff1133340 R11: ffffffff88999a03 R12: ffff88808d1849e8
R13: ffff88808d1849f2 R14: 00000000339133e8 R15: ffff88808d184100
lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:3841
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
_raw_spin_lock_irq+0x60/0x80 kernel/locking/spinlock.c:160
spin_lock_irq include/linux/spinlock.h:354 [inline]
flush_workqueue_prep_pwqs+0x1c5/0x590 kernel/workqueue.c:2633
flush_workqueue+0x54b/0x14c0 kernel/workqueue.c:2704
rxrpc_release_sock net/rxrpc/af_rxrpc.c:870 [inline]
rxrpc_release+0x409/0x830 net/rxrpc/af_rxrpc.c:901
__sock_release+0xd3/0x250 net/socket.c:579
sock_close+0x1b/0x30 net/socket.c:1139
__fput+0x2df/0x8d0 fs/file_table.c:278
____fput+0x16/0x20 fs/file_table.c:309
task_work_run+0x14a/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x411d31
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 94 19 00 00 c3 48
83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48
89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:0000000000a4fd90 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 000000000000000a RCX: 0000000000411d31
RDX: 0000000000000000 RSI: 0000000000743038 RDI: 0000000000000009
RBP: 0000000000000000 R08: ffffffff8100a15d R09: 0000000021576e54
R10: 0000000000a4fcc0 R11: 0000000000000293 R12: 0000000000000000
R13: 0000000000000001 R14: 00000000000000bd R15: 0000000000000005
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Eric Biggers]

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No repro, last seen 103 days ago, and other syzbot bugs in net/rxrpc have been
fixed since then.

#syz invalid