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Subject[PATCH tip/core/rcu 15/86] rcu: add tracing for RCU's kthread run states.
Date
From: Paul E. McKenney <paul.mckenney@linaro.org>

Add tracing to help debugging situations when RCU's kthreads are not
running but are supposed to be.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 11 ++++++++++-
kernel/rcutree.h | 11 +++++++++++
kernel/rcutree_plugin.h | 3 +++
kernel/rcutree_trace.c | 23 ++++++++++++++++++++---
4 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index eca6f05..a591694 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -91,8 +91,9 @@ EXPORT_SYMBOL_GPL(rcu_scheduler_active);
* handle all flavors of RCU.
*/
static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
+DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
-static DEFINE_PER_CPU(char, rcu_cpu_has_work);
+DEFINE_PER_CPU(char, rcu_cpu_has_work);
static char rcu_kthreads_spawnable;

static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
@@ -1563,11 +1564,13 @@ static int rcu_cpu_kthread(void *arg)
int cpu = (int)(long)arg;
unsigned long flags;
int spincnt = 0;
+ unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
wait_queue_head_t *wqp = &per_cpu(rcu_cpu_wq, cpu);
char work;
char *workp = &per_cpu(rcu_cpu_has_work, cpu);

for (;;) {
+ *statusp = RCU_KTHREAD_WAITING;
wait_event_interruptible(*wqp,
*workp != 0 || kthread_should_stop());
local_bh_disable();
@@ -1575,6 +1578,7 @@ static int rcu_cpu_kthread(void *arg)
local_bh_enable();
break;
}
+ *statusp = RCU_KTHREAD_RUNNING;
local_irq_save(flags);
work = *workp;
*workp = 0;
@@ -1587,10 +1591,12 @@ static int rcu_cpu_kthread(void *arg)
else
spincnt = 0;
if (spincnt > 10) {
+ *statusp = RCU_KTHREAD_YIELDING;
rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
spincnt = 0;
}
}
+ *statusp = RCU_KTHREAD_STOPPED;
return 0;
}

@@ -1637,10 +1643,12 @@ static int rcu_node_kthread(void *arg)
struct task_struct *t;

for (;;) {
+ rnp->node_kthread_status = RCU_KTHREAD_WAITING;
wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 ||
kthread_should_stop());
if (kthread_should_stop())
break;
+ rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
raw_spin_lock_irqsave(&rnp->lock, flags);
mask = rnp->wakemask;
rnp->wakemask = 0;
@@ -1661,6 +1669,7 @@ static int rcu_node_kthread(void *arg)
preempt_enable();
}
}
+ rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
return 0;
}

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index d49046c..67341db 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -89,6 +89,13 @@ struct rcu_dynticks {
atomic_t dynticks; /* Even value for dynticks-idle, else odd. */
};

+/* RCU's kthread states for tracing. */
+#define RCU_KTHREAD_STOPPED 0
+#define RCU_KTHREAD_RUNNING 1
+#define RCU_KTHREAD_WAITING 2
+#define RCU_KTHREAD_YIELDING 3
+#define RCU_KTHREAD_MAX 3
+
/*
* Definition for node within the RCU grace-period-detection hierarchy.
*/
@@ -152,6 +159,8 @@ struct rcu_node {
wait_queue_head_t boost_wq;
/* Wait queue on which to park the boost */
/* kthread. */
+ unsigned int boost_kthread_status;
+ /* State of boost_kthread_task for tracing. */
unsigned long n_tasks_boosted;
/* Total number of tasks boosted. */
unsigned long n_exp_boosts;
@@ -179,6 +188,8 @@ struct rcu_node {
wait_queue_head_t node_wq;
/* Wait queue on which to park the per-node */
/* kthread. */
+ unsigned int node_kthread_status;
+ /* State of node_kthread_task for tracing. */
} ____cacheline_internodealigned_in_smp;

/*
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 07d3464..22a6a46 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1198,11 +1198,13 @@ static int rcu_boost_kthread(void *arg)
int more2boost;

for (;;) {
+ rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
wait_event_interruptible(rnp->boost_wq, rnp->boost_tasks ||
rnp->exp_tasks ||
kthread_should_stop());
if (kthread_should_stop())
break;
+ rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
more2boost = rcu_boost(rnp);
if (more2boost)
spincnt++;
@@ -1213,6 +1215,7 @@ static int rcu_boost_kthread(void *arg)
spincnt = 0;
}
}
+ rnp->boost_kthread_status = RCU_KTHREAD_STOPPED;
return 0;
}

diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index afd262f..fc40e89 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -46,6 +46,16 @@
#define RCU_TREE_NONCORE
#include "rcutree.h"

+DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
+DECLARE_PER_CPU(char, rcu_cpu_has_work);
+
+static char convert_kthread_status(unsigned int kthread_status)
+{
+ if (kthread_status > RCU_KTHREAD_MAX)
+ return '?';
+ return "SRWY"[kthread_status];
+}
+
static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
@@ -64,7 +74,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks_fqs);
#endif /* #ifdef CONFIG_NO_HZ */
seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
- seq_printf(m, " ql=%ld qs=%c%c%c%c b=%ld",
+ seq_printf(m, " ql=%ld qs=%c%c%c%c kt=%d/%c b=%ld",
rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
@@ -73,6 +83,9 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
".W"[rdp->nxttail[RCU_DONE_TAIL] !=
rdp->nxttail[RCU_WAIT_TAIL]],
".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
+ per_cpu(rcu_cpu_has_work, rdp->cpu),
+ convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
+ rdp->cpu)),
rdp->blimit);
seq_printf(m, " ci=%lu co=%lu ca=%lu\n",
rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
@@ -130,7 +143,7 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks_fqs);
#endif /* #ifdef CONFIG_NO_HZ */
seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
- seq_printf(m, ",%ld,\"%c%c%c%c\",%ld", rdp->qlen,
+ seq_printf(m, ",%ld,\"%c%c%c%c\",%d,\"%c\",%ld", rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
@@ -138,6 +151,9 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
".W"[rdp->nxttail[RCU_DONE_TAIL] !=
rdp->nxttail[RCU_WAIT_TAIL]],
".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
+ per_cpu(rcu_cpu_has_work, rdp->cpu),
+ convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
+ rdp->cpu)),
rdp->blimit);
seq_printf(m, ",%lu,%lu,%lu\n",
rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
@@ -178,13 +194,14 @@ static const struct file_operations rcudata_csv_fops = {

static void print_one_rcu_node_boost(struct seq_file *m, struct rcu_node *rnp)
{
- seq_printf(m, "%d:%d tasks=%c%c%c%c ntb=%lu neb=%lu nnb=%lu "
+ seq_printf(m, "%d:%d tasks=%c%c%c%c kt=%c ntb=%lu neb=%lu nnb=%lu "
"j=%04x bt=%04x\n",
rnp->grplo, rnp->grphi,
"T."[list_empty(&rnp->blkd_tasks)],
"N."[!rnp->gp_tasks],
"E."[!rnp->exp_tasks],
"B."[!rnp->boost_tasks],
+ convert_kthread_status(rnp->boost_kthread_status),
rnp->n_tasks_boosted, rnp->n_exp_boosts,
rnp->n_normal_boosts,
(int)(jiffies & 0xffff),
--
1.7.3.2


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