From: Andrew Morton <akpm@linux-foundation.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Dmitry Vyukov <dvyukov@google.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kernel/hung_task.c: Break RCU locks based on jiffies.
Date: Fri, 14 Dec 2018 12:31:11 -0800 [thread overview]
Message-ID: <20181214123111.266cae10f71ea6b277d634c6@linux-foundation.org> (raw)
In-Reply-To: <1544800658-11423-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
On Sat, 15 Dec 2018 00:17:38 +0900 Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:
> check_hung_uninterruptible_tasks() is currently calling rcu_lock_break()
> for every 1024 threads. But check_hung_task() is very slow if printk()
> was called, and is very fast otherwise. If many threads within some 1024
> threads called printk(), the RCU grace period might be extended enough
> to trigger RCU stall warnings. Therefore, calling rcu_lock_break() for
> every some fixed jiffies will be safer.
>
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -34,7 +34,7 @@
> * is disabled during the critical section. It also controls the size of
> * the RCU grace period. So it needs to be upper-bound.
> */
> -#define HUNG_TASK_BATCHING 1024
> +#define HUNG_TASK_LOCK_BREAK (HZ / 10)
This won't work correctly if rcu_cpu_stall_timeout is set to something
stupidly small. Perhaps is would be better to make this code aware of
the current rcu_cpu_stall_timeout setting?
next prev parent reply other threads:[~2018-12-14 20:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-14 15:17 [PATCH] kernel/hung_task.c: Break RCU locks based on jiffies Tetsuo Handa
2018-12-14 15:58 ` Paul E. McKenney
2018-12-14 20:31 ` Andrew Morton [this message]
2018-12-14 21:01 ` Paul E. McKenney
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