WARNING: bad unlock balance in migration_cpu_stop

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: bfc52594 ANDROID: sched/walt: Fix lockdep assert issue
git tree: android-4.14
console output: https://syzkaller.appspot.com/x/log.txt?x=1652e5a7400000
kernel config: https://syzkaller.appspot.com/x/.config?x=dfccb7ab0265fcc5
dashboard link: https://syzkaller.appspot.com/bug?extid=6f0dc342c4fbc8394767
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13b165b0c00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12e04cd4c00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6f0dc3...@syzkaller.appspotmail.com

EXT4-fs (loop0): VFS: Can't find ext4 filesystem
EXT4-fs (loop0): VFS: Can't find ext4 filesystem
EXT4-fs (loop0): VFS: Can't find ext4 filesystem
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EXT4-fs (loop0): VFS: Can't find ext4 filesystem
WARNING: bad unlock balance detected!
4.14.99+ #12 Not tainted
-------------------------------------
migration/1/16 is trying to release lock (&rq->lock) at:
[<ffffffff9616db1d>] migration_cpu_stop+0x2dd/0x430 kernel/sched/core.c:1036
but there are no more locks to release!

other info that might help us debug this:
1 lock held by migration/1/16:
#0: (&p->pi_lock){-.-.}, at: [<ffffffff9616d921>]
migration_cpu_stop+0xe1/0x430 kernel/sched/core.c:1027

stack backtrace:
CPU: 1 PID: 16 Comm: migration/1 Not tainted 4.14.99+ #12
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xb9/0x10e lib/dump_stack.c:53
print_unlock_imbalance_bug kernel/locking/lockdep.c:3548 [inline]
print_unlock_imbalance_bug.cold+0x110/0x11f kernel/locking/lockdep.c:3525
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