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Date: Thu, 14 Aug 2014 17:39:54 -0400
From: Pranith Kumar <bobby.prani@...il.com>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Lai Jiangshan <laijs@...fujitsu.com>,
Dipankar Sarma <dipankar@...ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Josh Triplett <josh@...htriplett.org>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
David Howells <dhowells@...hat.com>,
Eric Dumazet <edumazet@...gle.com>, dvhart@...ux.intel.com,
Frédéric Weisbecker <fweisbec@...il.com>,
Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v5 tip/core/rcu 08/16] rcu: Add stall-warning checks for RCU-tasks
On Mon, Aug 11, 2014 at 6:48 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
>
> This commit adds a three-minute RCU-tasks stall warning. The actual
> time is controlled by the boot/sysfs parameter rcu_task_stall_timeout,
> with values less than or equal to zero disabling the stall warnings.
> The default value is three minutes, which means that the tasks that
> have not yet responded will get their stacks dumped every ten minutes,
> until they pass through a voluntary context switch.
>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Something about 3 minutes and 10 minutes is mixed up here!
> ---
> Documentation/kernel-parameters.txt | 5 +++++
> kernel/rcu/update.c | 27 ++++++++++++++++++++++++---
> 2 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 910c3829f81d..8cdbde7b17f5 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2921,6 +2921,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> rcupdate.rcu_cpu_stall_timeout= [KNL]
> Set timeout for RCU CPU stall warning messages.
>
> + rcupdate.rcu_task_stall_timeout= [KNL]
> + Set timeout in jiffies for RCU task stall warning
> + messages. Disable with a value less than or equal
> + to zero.
> +
> rdinit= [KNL]
> Format: <full_path>
> Run specified binary instead of /init from the ramdisk,
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index 8f53a41dd9ee..f1535404a79e 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -374,7 +374,7 @@ static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
> DEFINE_SRCU(tasks_rcu_exit_srcu);
>
> /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
> -static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 3;
> +static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
> module_param(rcu_task_stall_timeout, int, 0644);
>
> /* Post an RCU-tasks callback. */
> @@ -449,7 +449,8 @@ void rcu_barrier_tasks(void)
> EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
>
> /* See if tasks are still holding out, complain if so. */
> -static void check_holdout_task(struct task_struct *t)
> +static void check_holdout_task(struct task_struct *t,
> + bool needreport, bool *firstreport)
> {
> if (!ACCESS_ONCE(t->rcu_tasks_holdout) ||
> t->rcu_tasks_nvcsw != ACCESS_ONCE(t->nvcsw) ||
> @@ -457,7 +458,15 @@ static void check_holdout_task(struct task_struct *t)
> ACCESS_ONCE(t->rcu_tasks_holdout) = 0;
> list_del_rcu(&t->rcu_tasks_holdout_list);
> put_task_struct(t);
> + return;
> }
> + if (!needreport)
> + return;
> + if (*firstreport) {
> + pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
> + *firstreport = false;
> + }
> + sched_show_task(t);
> }
>
> /* RCU-tasks kthread that detects grace periods and invokes callbacks. */
> @@ -465,6 +474,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
> {
> unsigned long flags;
> struct task_struct *g, *t;
> + unsigned long lastreport;
> struct rcu_head *list;
> struct rcu_head *next;
> LIST_HEAD(rcu_tasks_holdouts);
> @@ -543,13 +553,24 @@ static int __noreturn rcu_tasks_kthread(void *arg)
> * of holdout tasks, removing any that are no longer
> * holdouts. When the list is empty, we are done.
> */
> + lastreport = jiffies;
> while (!list_empty(&rcu_tasks_holdouts)) {
> + bool firstreport;
> + bool needreport;
> + int rtst;
> +
> schedule_timeout_interruptible(HZ);
> + rtst = ACCESS_ONCE(rcu_task_stall_timeout);
> + needreport = rtst > 0 &&
> + time_after(jiffies, lastreport + rtst);
> + if (needreport)
> + lastreport = jiffies;
> + firstreport = true;
> WARN_ON(signal_pending(current));
> rcu_read_lock();
> list_for_each_entry_rcu(t, &rcu_tasks_holdouts,
> rcu_tasks_holdout_list)
> - check_holdout_task(t);
> + check_holdout_task(t, needreport, &firstreport);
> rcu_read_unlock();
> }
>
> --
> 1.8.1.5
>
--
Pranith
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