WARNING in get_signal

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    fcadab74 Merge tag 'drm-fixes-2020-10-01-1' of git://anong..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=116865bd900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=89ab6a0c48f30b49
dashboard link: https://syzkaller.appspot.com/bug?extid=3485e3773f7da290eecc
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1211120b900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16474c67900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3485e3773f7da290eecc@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
WARNING: CPU: 1 PID: 6899 at kernel/signal.c:2431 do_jobctl_trap kernel/signal.c:2431 [inline]
WARNING: CPU: 1 PID: 6899 at kernel/signal.c:2431 get_signal+0x1b5c/0x1f00 kernel/signal.c:2621
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 6899 Comm: syz-executor116 Not tainted 5.9.0-rc7-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+0x382/0x7fb kernel/panic.c:231
 __warn.cold+0x20/0x4b 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:do_jobctl_trap kernel/signal.c:2431 [inline]
RIP: 0010:get_signal+0x1b5c/0x1f00 kernel/signal.c:2621
Code: 00 48 c7 c2 40 da 8a 88 be d1 09 00 00 48 c7 c7 a0 da 8a 88 c6 05 09 8c 09 0a 01 e8 43 97 11 00 e9 42 f5 ff ff e8 14 78 2b 00 <0f> 0b 41 bc 00 80 00 00 e9 49 f9 ff ff 4c 89 ef e8 bf 4d 6c 00 e9
RSP: 0018:ffffc90005537ce8 EFLAGS: 00010093
RAX: 0000000000000000 RBX: 0000000100000000 RCX: ffffffff814abfc3
RDX: ffff88809315c580 RSI: ffffffff814ac67c RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000001 R09: ffff88809315ca0f
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000008000
R13: 0000000000000000 R14: 0000000000000000 R15: dffffc0000000000
 arch_do_signal+0x82/0x2520 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0x1ae/0x200 kernel/entry/common.c:192
 syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:267
 ret_from_fork+0x15/0x30 arch/x86/entry/entry_64.S:287
RIP: 0033:0x446809
Code: e8 5c b3 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 0f 83 8b 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fbb8cdd1db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: 0000000000000000 RBX: 00000000006dbc28 RCX: 0000000000446809
RDX: 9999999999999999 RSI: 0000000000000000 RDI: 000000000007a900
RBP: 00000000006dbc20 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc2c
R13: 00007ffeca1e9fef R14: 00007fbb8cdd29c0 R15: 20c49ba5e353f7cf
Shutting down cpus with NMI
Kernel Offset: disabled
Rebooting in 86400 seconds..


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