lkml.org 
[lkml]   [2019]   [Jun]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC] rcu: Warn that rcu ktheads cannot be spawned
Date
Hello rcu folks,

I thought it'd better to announce it if those spawnings fail because of
!rcu_scheduler_fully_active.

Of course, with the current code, it never happens though.

Thoughts?

Thanks,
Byungchul

---8<---
From 58a33a85c70f82c406319b4752af95cf6ceb73a3 Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.park@lge.com>
Date: Mon, 24 Jun 2019 17:08:26 +0900
Subject: [RFC] rcu: Warn that rcu ktheads cannot be spawned

In case that rcu ktheads cannot be spawned due to
!rcu_scheduler_fully_active, it'd be better to anounce it.

While at it, because the return value of rcu_spawn_one_boost_kthread()
is not used any longer, changed the return type from int to void.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/rcu/tree_plugin.h | 31 +++++++++++++++++++------------
1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1102765..7d74193 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1131,7 +1131,7 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
* already exist. We only create this kthread for preemptible RCU.
* Returns zero if all is well, a negated errno otherwise.
*/
-static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
+static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
{
int rnp_index = rnp - rcu_get_root();
unsigned long flags;
@@ -1139,25 +1139,24 @@ static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
struct task_struct *t;

if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
- return 0;
+ return;

- if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
- return 0;
+ if (rcu_rnp_online_cpus(rnp) == 0)
+ return;

rcu_state.boost = 1;
if (rnp->boost_kthread_task != NULL)
- return 0;
+ return;
t = kthread_create(rcu_boost_kthread, (void *)rnp,
"rcub/%d", rnp_index);
if (IS_ERR(t))
- return PTR_ERR(t);
+ return;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->boost_kthread_task = t;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
- return 0;
}

static void rcu_cpu_kthread_setup(unsigned int cpu)
@@ -1264,8 +1263,12 @@ static void __init rcu_spawn_boost_kthreads(void)
per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__))
return;
+
+ if (WARN_ON(!rcu_scheduler_fully_active))
+ return;
+
rcu_for_each_leaf_node(rnp)
- (void)rcu_spawn_one_boost_kthread(rnp);
+ rcu_spawn_one_boost_kthread(rnp);
}

static void rcu_prepare_kthreads(int cpu)
@@ -1273,9 +1276,11 @@ static void rcu_prepare_kthreads(int cpu)
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_node *rnp = rdp->mynode;

+ if (WARN_ON(!rcu_scheduler_fully_active))
+ return;
+
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
- if (rcu_scheduler_fully_active)
- (void)rcu_spawn_one_boost_kthread(rnp);
+ rcu_spawn_one_boost_kthread(rnp);
}

#else /* #ifdef CONFIG_RCU_BOOST */
@@ -2198,8 +2203,10 @@ static void rcu_spawn_one_nocb_kthread(int cpu)
*/
static void rcu_spawn_cpu_nocb_kthread(int cpu)
{
- if (rcu_scheduler_fully_active)
- rcu_spawn_one_nocb_kthread(cpu);
+ if (WARN_ON(!rcu_scheduler_fully_active))
+ return;
+
+ rcu_spawn_one_nocb_kthread(cpu);
}

/*
--
1.9.1
\
 
 \ /
  Last update: 2019-06-24 10:58    [W:0.086 / U:6.996 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site