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Date:   Fri, 16 Jun 2023 09:39:57 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Zqiang <qiang.zhang1211@gmail.com>
Cc:     frederic@kernel.org, joel@joelfernandes.org,
        quic_neeraju@quicinc.com, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rcuscale: Move schedule_timeout _uninterruptible to
 _idle in rcu_scale_writer()
Message-ID: <a05a940b-208b-4a06-b3fd-f8cb59bcab3f@paulmck-laptop>
Reply-To: paulmck@kernel.org
References: <20230616073926.24462-1-qiang.zhang1211@gmail.com>
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On Fri, Jun 16, 2023 at 03:39:26PM +0800, Zqiang wrote:
> The rcuscale.holdoff can be used to delay the start of rcu_scale_writer
> kthread, however, if the rcuscale.holdoff is set and the timeout is greater
> than the hung_task_timeout_secs, can trigger the hung-task timeout:
> 
> 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>

Good catch, queued, thank you!

							Thanx, Paul

> ---
>  kernel/rcu/rcuscale.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
> index a0eae1900708..ffdb30495e3c 100644
> --- a/kernel/rcu/rcuscale.c
> +++ b/kernel/rcu/rcuscale.c
> @@ -469,7 +469,7 @@ rcu_scale_writer(void *arg)
>  	sched_set_fifo_low(current);
>  
>  	if (holdoff)
> -		schedule_timeout_uninterruptible(holdoff * HZ);
> +		schedule_timeout_idle(holdoff * HZ);
>  
>  	/*
>  	 * Wait until rcu_end_inkernel_boot() is called for normal GP tests
> -- 
> 2.17.1
>