WARNING in task_participate_group_stop

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: cef9f8d2 Revert "ANDROID: overlayfs: override_creds=off op..
git tree: android-4.14
console output: https://syzkaller.appspot.com/x/log.txt?x=10eec05f200000
kernel config: https://syzkaller.appspot.com/x/.config?x=322dd7397c84f390
dashboard link: https://syzkaller.appspot.com/bug?extid=11a2061959c90f1df73e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15101177200000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12f3749d200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+11a206...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
audit: type=1400 audit(1551895949.038:7): avc: denied { map } for
pid=1785 comm="syz-executor650" path="/root/syz-executor650351011"
dev="sda1" ino=16482 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1800 at kernel/signal.c:349
task_participate_group_stop+0x1b3/0x210 kernel/signal.c:349
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 1800 Comm: 5 Not tainted 4.14.105+ #25
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xb9/0x10e lib/dump_stack.c:53
panic+0x1d9/0x3c2 kernel/panic.c:182
__warn.cold+0x2f/0x3b kernel/panic.c:546
Kernel Offset: 0x9200000 from 0xffffffff81000000 (relocation range:
0xffffffff80000000-0xffffffffbfffffff)
Rebooting in 86400 seconds..


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