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SubjectWARNING: locking bug in __atomic_notifier_call_chain
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Hello,

syzbot found the following issue on:

HEAD commit: a8205e31 Merge tag 'io_uring-5.9-2020-09-06' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16f5880d900000
kernel config: https://syzkaller.appspot.com/x/.config?x=9b0e48dac62b2233
dashboard link: https://syzkaller.appspot.com/bug?extid=ff42f38fc7fac3423b16
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17734d95900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=167c90dd900000

Bisection is inconclusive: the issue happens on the oldest tested release.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13982159900000
final oops: https://syzkaller.appspot.com/x/report.txt?x=10582159900000
console output: https://syzkaller.appspot.com/x/log.txt?x=17982159900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ff42f38fc7fac3423b16@syzkaller.appspotmail.com

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(chain_key != INITIAL_CHAIN_KEY)
WARNING: CPU: 0 PID: 10424 at kernel/locking/lockdep.c:4404 __lock_acquire+0x1a0f/0x5570 kernel/locking/lockdep.c:4404
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 10424 Comm: Not tainted 5.9.0-rc3-syzkaller #0
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+0x198/0x1fd lib/dump_stack.c:118
panic+0x347/0x7c0 kernel/panic.c:231
__warn.cold+0x20/0x46 kernel/panic.c:600
report_bug+0x1bd/0x210 lib/bug.c:198
handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:__lock_acquire+0x1a0f/0x5570 kernel/locking/lockdep.c:4404
Code: d2 0f 85 d1 2f 00 00 44 8b 3d d5 81 58 09 45 85 ff 0f 85 73 f3 ff ff 48 c7 c6 00 d4 4b 88 48 c7 c7 20 a8 4b 88 e8 43 32 eb ff <0f> 0b e9 5c f3 ff ff 48 c7 c2 60 31 97 8c 48 b8 00 00 00 00 00 fc
RSP: 0018:ffffc900055472e0 EFLAGS: 00010086
RAX: 0000000000000000 RBX: 0000000007000000 RCX: 0000000000000000
RDX: ffff888000132000 RSI: ffffffff815db9a7 RDI: fffff52000aa8e4e
RBP: ffff8880001328e8 R08: 0000000000000000 R09: ffffffff89bcb4a3
R10: 00000000000005a3 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: ffff888000132000 R15: 0000000000000000
lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
rcu_lock_acquire include/linux/rcupdate.h:241 [inline]
rcu_read_lock include/linux/rcupdate.h:634 [inline]
__atomic_notifier_call_chain+0x48/0x180 kernel/notifier.c:172
notify_write drivers/tty/vt/vt.c:264 [inline]
cr drivers/tty/vt/vt.c:1517 [inline]
vc_con_write_normal drivers/tty/vt/vt.c:2805 [inline]
do_con_write+0xed5/0x1d70 drivers/tty/vt/vt.c:2910
con_write+0x22/0xb0 drivers/tty/vt/vt.c:3250
process_output_block drivers/tty/n_tty.c:595 [inline]
n_tty_write+0x3ce/0xf80 drivers/tty/n_tty.c:2333
do_tty_write drivers/tty/tty_io.c:962 [inline]
tty_write+0x4d9/0x870 drivers/tty/tty_io.c:1046
__kernel_write+0x199/0x570 fs/read_write.c:528
write_pipe_buf+0x153/0x1f0 fs/splice.c:799
splice_from_pipe_feed fs/splice.c:502 [inline]
__splice_from_pipe+0x3dc/0x830 fs/splice.c:626
splice_from_pipe fs/splice.c:661 [inline]
default_file_splice_write fs/splice.c:811 [inline]
do_splice_from fs/splice.c:847 [inline]
direct_splice_actor+0x228/0x2f0 fs/splice.c:1016
splice_direct_to_actor+0x38c/0x980 fs/splice.c:971
do_splice_direct+0x1b3/0x280 fs/splice.c:1059
do_sendfile+0x55f/0xd40 fs/read_write.c:1540
__do_sys_sendfile64 fs/read_write.c:1601 [inline]
__se_sys_sendfile64 fs/read_write.c:1587 [inline]
__x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1587
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x446ac9
Code: Bad RIP value.
RSP: 002b:00007f7bb7b3cd18 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00000000006dbc58 RCX: 0000000000446ac9
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000004
RBP: 00000000006dbc50 R08: 65732f636f72702f R09: 65732f636f72702f
R10: 0800000080004103 R11: 0000000000000246 R12: 00000000006dbc5c
R13: 00007f7bb7b3cd20 R14: 00007f7bb7b3cd20 R15: 20c49ba5e353f7cf
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

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