The rcuscale.holdoff module parameter can be used to delay the start
of rcu_scale_writer() kthread.  However, the hung-task timeout will
trigger when the timeout specified by rcuscale.holdoff is greater than
hung_task_timeout_secs:

runqemu kvm nographic slirp qemuparams="-smp 4 -m 2048M"
bootparams="rcuscale.shutdown=0 rcuscale.holdoff=300"

[  247.071753] INFO: task rcu_scale_write:59 blocked for more than 122 seconds.
[  247.072529]       Not tainted 6.4.0-rc1-00134-gb9ed6de8d4ff #7
[  247.073400] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  247.074331] task:rcu_scale_write state:D stack:30144 pid:59    ppid:2      flags:0x00004000
[  247.075346] Call Trace:
[  247.075660]  <TASK>
[  247.075965]  __schedule+0x635/0x1280
[  247.076448]  ? __pfx___schedule+0x10/0x10
[  247.076967]  ? schedule_timeout+0x2dc/0x4d0
[  247.077471]  ? __pfx_lock_release+0x10/0x10
[  247.078018]  ? enqueue_timer+0xe2/0x220
[  247.078522]  schedule+0x84/0x120
[  247.078957]  schedule_timeout+0x2e1/0x4d0
[  247.079447]  ? __pfx_schedule_timeout+0x10/0x10
[  247.080032]  ? __pfx_rcu_scale_writer+0x10/0x10
[  247.080591]  ? __pfx_process_timeout+0x10/0x10
[  247.081163]  ? __pfx_sched_set_fifo_low+0x10/0x10
[  247.081760]  ? __pfx_rcu_scale_writer+0x10/0x10
[  247.082287]  rcu_scale_writer+0x6b1/0x7f0
[  247.082773]  ? mark_held_locks+0x29/0xa0
[  247.083252]  ? __pfx_rcu_scale_writer+0x10/0x10
[  247.083865]  ? __pfx_rcu_scale_writer+0x10/0x10
[  247.084412]  kthread+0x179/0x1c0
[  247.084759]  ? __pfx_kthread+0x10/0x10
[  247.085098]  ret_from_fork+0x2c/0x50
[  247.085433]  </TASK>

This commit therefore replaces schedule_timeout_uninterruptible() with
schedule_timeout_idle().
Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>