[bug-report] WARNING in sched_tick_remote

[Hui Tang]

Hi,

An warning happen in sched_tick_remote when we do syzkaller test.
The syzkaller test run in a qemu with 4 cpus, and nohz_full=3.

The warn triggered by WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3).

	static void sched_tick_remote(struct work_struct *work)
	{
	[...]
			if (!is_idle_task(curr)) {
					/*
					 * Make sure the next tick runs within a reasonable
					 * amount of time.
					 */
					delta = rq_clock_task(rq) - curr->se.exec_start;
					WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
			}
	[...]
	}

I debug it and find that a syzkaller thread keep in kernel mode
more than 3s. And all unbound kworkers run on the same cpu as the
syzkaller thread. The kworker thread doing sched_tick_remote
is scheduled more than 3s since last run.

WARN log as follows:

WARNING: CPU: 2 PID: 23866 at kernel/sched/core.c:4142 queued_spin_lock arch/arm64/include/asm/paravirt.h:51 [inline]
WARNING: CPU: 2 PID: 23866 at kernel/sched/core.c:4142 do_raw_spin_lock include/linux/spinlock.h:183 [inline]
WARNING: CPU: 2 PID: 23866 at kernel/sched/core.c:4142 __raw_spin_lock_irq include/linux/spinlock_api_smp.h:129 [inline]
WARNING: CPU: 2 PID: 23866 at kernel/sched/core.c:4142 rq_lock_irq kernel/sched/sched.h:1373 [inline]
WARNING: CPU: 2 PID: 23866 at kernel/sched/core.c:4142 sched_tick_remote+0x384/0x400 kernel/sched/core.c:4129
Modules linked in:
CPU: 2 PID: 23866 Comm: kworker/u8:3 Not tainted 5.10.0-02029-gf83322d59c08-dirty #1
Hardware name: linux,dummy-virt (DT)
Workqueue: events_unbound sched_tick_remote
pstate: 20400085 (nzCv daIf +PAN -UAO -TCO BTYPE=--)
pc : sched_tick_remote+0x384/0x400 kernel/sched/core.c:4142
lr : sched_tick_remote+0x1e4/0x400 kernel/sched/core.c:4141
sp : ffffa00019347ba0
x29: ffffa00019347ba0 x28: ffff0000e2a8c110
x27: 0000000000000000 x26: ffffa00014af6e88
x25: ffff000224cbc4f8 x24: ffffa00014b45840
x23: 000000013afb24ae x22: 1ffff40003268f80
x21: ffff000224cbfa28 x20: ffff0000c0e53e80
x19: ffff000224cbbb40 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000
x15: 0000000000000000 x14: 0000000000000000
x13: 0000000000000002 x12: ffff940003268f85
x11: 1ffff40003268f84 x10: ffff940003268f84
x9 : ffffa000101bece8 x8 : 0000000000000003
x7 : 0000000000000001 x6 : ffff940003268f84
x5 : ffff0000d63229c0 x4 : dfffa00000000000
x3 : ffffa000101c33f4 x2 : 0000000000000007
x1 : 0000026d1ef2161e x0 : 00000000b2d05e00
Call trace:
 queued_spin_lock arch/arm64/include/asm/paravirt.h:51 [inline]
 do_raw_spin_lock include/linux/spinlock.h:183 [inline]
 __raw_spin_lock_irq include/linux/spinlock_api_smp.h:129 [inline]
 rq_lock_irq kernel/sched/sched.h:1373 [inline]
 sched_tick_remote+0x384/0x400 kernel/sched/core.c:4129
 process_one_work+0x474/0xb20 kernel/workqueue.c:2280
 worker_thread+0x120/0x92c kernel/workqueue.c:2426
 kthread+0x20c/0x25c kernel/kthread.c:313
 ret_from_fork+0x10/0x18 arch/arm64/kernel/entry.S:1034