TITLE: possible deadlock in tick_handler
TYPE: LOCKDEP

[ 1740.381206][    C0] WARNING: possible circular locking dependency detected
[ 1740.381209][    C0] 4.15.0+ #6 Not tainted
[ 1740.381215][    C0] ------------------------------------------------------
[ 1740.381219][    C0] syz-executor.2/31457 is trying to acquire lock:
[ 1740.381222][    C0] ffffffff8600aef8 ((console_sem).lock){-.-.}, at: down_trylock+0x13/0x70
[ 1740.381235][    C0] 
[ 1740.381239][    C0] but task is already holding lock:
[ 1740.381242][    C0] ffff88006c849558 (&rq->lock){-.-.}, at: tick_handler+0x17e/0xb00
[ 1740.381254][    C0] 
[ 1740.381259][    C0] which lock already depends on the new lock.
[ 1740.381261][    C0] 
[ 1740.381262][    C0] 
[ 1740.381266][    C0] the existing dependency chain (in reverse order) is:
[ 1740.381268][    C0] 
[ 1740.381270][    C0] -> #2 (&rq->lock){-.-.}:
[ 1740.381280][    C0]        _raw_spin_lock+0x2b/0x40
[ 1740.381283][    C0]        task_fork_fair+0x41/0x3c0
[ 1740.381286][    C0]        sched_fork+0x505/0xd70
[ 1740.381290][    C0]        copy_process+0x1c8a/0x6ef0
[ 1740.381292][    C0]        _do_fork+0xf4/0x750
[ 1740.381296][    C0]        kernel_thread+0xc6/0x100
[ 1740.381299][    C0]        rest_init+0x24/0x1da
[ 1740.381302][    C0]        start_kernel+0x824/0x85f
[ 1740.381722][    C0] Call Trace:
[ 1740.381729][    C0]  dump_stack+0x175/0x1dd
[ 1740.381733][    C0]  print_circular_bug.cold+0x162/0x171
[ 1740.381737][    C0]  check_noncircular+0x304/0x400
[ 1740.381758][    C0]  __lock_acquire+0x2522/0x5470
[ 1740.381769][    C0]  lock_acquire+0x1d8/0x770
[ 1740.381789][    C0]  _raw_spin_lock_irqsave+0x92/0xd0
[ 1740.381796][    C0]  down_trylock+0x13/0x70
[ 1740.381804][    C0]  __down_trylock_console_sem+0xa8/0x210
[ 1740.381808][    C0]  vprintk_emit+0x2c2/0x770
[ 1740.381811][    C0]  vprintk_default+0x28/0x30
[ 1740.381815][    C0]  vprintk_func+0x7a/0x120
[ 1740.381818][    C0]  printk+0xba/0xed
[ 1740.381832][    C0]  tick_handler.cold+0x8c/0x258
