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rcu: add tracing for RCU's kthread run states.
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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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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Paul E. McKenney authored and Paul E. McKenney committed May 6, 2011
1 parent 0ac3d13 commit d71df90
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Showing 4 changed files with 44 additions and 4 deletions.
11 changes: 10 additions & 1 deletion kernel/rcutree.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down Expand Up @@ -1563,18 +1564,21 @@ 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();
if (rcu_cpu_kthread_should_stop(cpu)) {
local_bh_enable();
break;
}
*statusp = RCU_KTHREAD_RUNNING;
local_irq_save(flags);
work = *workp;
*workp = 0;
Expand All @@ -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;
}

Expand Down Expand Up @@ -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;
Expand All @@ -1661,6 +1669,7 @@ static int rcu_node_kthread(void *arg)
preempt_enable();
}
}
rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
return 0;
}

Expand Down
11 changes: 11 additions & 0 deletions kernel/rcutree.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
*/
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;

/*
Expand Down
3 changes: 3 additions & 0 deletions kernel/rcutree_plugin.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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++;
Expand All @@ -1213,6 +1215,7 @@ static int rcu_boost_kthread(void *arg)
spincnt = 0;
}
}
rnp->boost_kthread_status = RCU_KTHREAD_STOPPED;
return 0;
}

Expand Down
23 changes: 20 additions & 3 deletions kernel/rcutree_trace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
Expand All @@ -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]],
Expand All @@ -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);
Expand Down Expand Up @@ -130,14 +143,17 @@ 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] !=
rdp->nxttail[RCU_NEXT_READY_TAIL]],
".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);
Expand Down Expand Up @@ -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),
Expand Down

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