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linux/kernel/rcutree_trace.c
Paul E. McKenney e4cc1f22b2 rcu: Simplify quiescent-state accounting 
There is often a delay between the time that a CPU passes through a
quiescent state and the time that this quiescent state is reported to the
RCU core.  It is quite possible that the grace period ended before the
quiescent state could be reported, for example, some other CPU might have
deduced that this CPU passed through dyntick-idle mode.  It is critically
important that quiescent state be counted only against the grace period
that was in effect at the time that the quiescent state was detected.

Previously, this was handled by recording the number of the last grace
period to complete when passing through a quiescent state.  The RCU
core then checks this number against the current value, and rejects
the quiescent state if there is a mismatch.  However, one additional
possibility must be accounted for, namely that the quiescent state was
recorded after the prior grace period completed but before the current
grace period started.  In this case, the RCU core must reject the
quiescent state, but the recorded number will match.  This is handled
when the CPU becomes aware of a new grace period -- at that point,
it invalidates any prior quiescent state.

This works, but is a bit indirect.  The new approach records the current
grace period, and the RCU core checks to see (1) that this is still the
current grace period and (2) that this grace period has not yet ended.
This approach simplifies reasoning about correctness, and this commit
changes over to this new approach.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-09-28 21:38:22 -07:00

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/*
* Read-Copy Update tracing for classic implementation
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright IBM Corporation, 2008
*
* Papers: http://www.rdrop.com/users/paulmck/RCU
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
*
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/module.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/debugfs.h>
#include <linux/seq_file.h>
#define RCU_TREE_NONCORE
#include "rcutree.h"
#ifdef CONFIG_RCU_BOOST
static char convert_kthread_status(unsigned int kthread_status)
{
if (kthread_status > RCU_KTHREAD_MAX)
return '?';
return "SRWOY"[kthread_status];
}
#endif /* #ifdef CONFIG_RCU_BOOST */
static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
return;
seq_printf(m, "%3d%cc=%lu g=%lu pq=%d pgp=%lu qp=%d",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? '!' : ' ',
rdp->completed, rdp->gpnum,
rdp->passed_quiesce, rdp->passed_quiesce_gpnum,
rdp->qs_pending);
#ifdef CONFIG_NO_HZ
seq_printf(m, " dt=%d/%d/%d df=%lu",
atomic_read(&rdp->dynticks->dynticks),
rdp->dynticks->dynticks_nesting,
rdp->dynticks->dynticks_nmi_nesting,
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",
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]]);
#ifdef CONFIG_RCU_BOOST
seq_printf(m, " kt=%d/%c/%d ktl=%x",
per_cpu(rcu_cpu_has_work, rdp->cpu),
convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
rdp->cpu)),
per_cpu(rcu_cpu_kthread_cpu, rdp->cpu),
per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff);
#endif /* #ifdef CONFIG_RCU_BOOST */
seq_printf(m, " b=%ld", rdp->blimit);
seq_printf(m, " ci=%lu co=%lu ca=%lu\n",
rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
}
#define PRINT_RCU_DATA(name, func, m) \
do { \
int _p_r_d_i; \
\
for_each_possible_cpu(_p_r_d_i) \
func(m, &per_cpu(name, _p_r_d_i)); \
} while (0)
static int show_rcudata(struct seq_file *m, void *unused)
{
#ifdef CONFIG_TREE_PREEMPT_RCU
seq_puts(m, "rcu_preempt:\n");
PRINT_RCU_DATA(rcu_preempt_data, print_one_rcu_data, m);
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
seq_puts(m, "rcu_sched:\n");
PRINT_RCU_DATA(rcu_sched_data, print_one_rcu_data, m);
seq_puts(m, "rcu_bh:\n");
PRINT_RCU_DATA(rcu_bh_data, print_one_rcu_data, m);
return 0;
}
static int rcudata_open(struct inode *inode, struct file *file)
{
return single_open(file, show_rcudata, NULL);
}
static const struct file_operations rcudata_fops = {
.owner = THIS_MODULE,
.open = rcudata_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
return;
seq_printf(m, "%d,%s,%lu,%lu,%d,%lu,%d",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? "\"N\"" : "\"Y\"",
rdp->completed, rdp->gpnum,
rdp->passed_quiesce, rdp->passed_quiesce_gpnum,
rdp->qs_pending);
#ifdef CONFIG_NO_HZ
seq_printf(m, ",%d,%d,%d,%lu",
atomic_read(&rdp->dynticks->dynticks),
rdp->dynticks->dynticks_nesting,
rdp->dynticks->dynticks_nmi_nesting,
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\"", 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]]);
#ifdef CONFIG_RCU_BOOST
seq_printf(m, ",%d,\"%c\"",
per_cpu(rcu_cpu_has_work, rdp->cpu),
convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
rdp->cpu)));
#endif /* #ifdef CONFIG_RCU_BOOST */
seq_printf(m, ",%ld", rdp->blimit);
seq_printf(m, ",%lu,%lu,%lu\n",
rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
}
static int show_rcudata_csv(struct seq_file *m, void *unused)
{
seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pgp\",\"pq\",");
#ifdef CONFIG_NO_HZ
seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
#endif /* #ifdef CONFIG_NO_HZ */
seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\"");
#ifdef CONFIG_RCU_BOOST
seq_puts(m, "\"kt\",\"ktl\"");
#endif /* #ifdef CONFIG_RCU_BOOST */
seq_puts(m, ",\"b\",\"ci\",\"co\",\"ca\"\n");
#ifdef CONFIG_TREE_PREEMPT_RCU
seq_puts(m, "\"rcu_preempt:\"\n");
PRINT_RCU_DATA(rcu_preempt_data, print_one_rcu_data_csv, m);
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
seq_puts(m, "\"rcu_sched:\"\n");
PRINT_RCU_DATA(rcu_sched_data, print_one_rcu_data_csv, m);
seq_puts(m, "\"rcu_bh:\"\n");
PRINT_RCU_DATA(rcu_bh_data, print_one_rcu_data_csv, m);
return 0;
}
static int rcudata_csv_open(struct inode *inode, struct file *file)
{
return single_open(file, show_rcudata_csv, NULL);
}
static const struct file_operations rcudata_csv_fops = {
.owner = THIS_MODULE,
.open = rcudata_csv_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
#ifdef CONFIG_RCU_BOOST
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 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),
(int)(rnp->boost_time & 0xffff));
seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu nb=%lu ny=%lu nos=%lu\n",
" balk",
rnp->n_balk_blkd_tasks,
rnp->n_balk_exp_gp_tasks,
rnp->n_balk_boost_tasks,
rnp->n_balk_notblocked,
rnp->n_balk_notyet,
rnp->n_balk_nos);
}
static int show_rcu_node_boost(struct seq_file *m, void *unused)
{
struct rcu_node *rnp;
rcu_for_each_leaf_node(&rcu_preempt_state, rnp)
print_one_rcu_node_boost(m, rnp);
return 0;
}
static int rcu_node_boost_open(struct inode *inode, struct file *file)
{
return single_open(file, show_rcu_node_boost, NULL);
}
static const struct file_operations rcu_node_boost_fops = {
.owner = THIS_MODULE,
.open = rcu_node_boost_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
/*
* Create the rcuboost debugfs entry. Standard error return.
*/
static int rcu_boost_trace_create_file(struct dentry *rcudir)
{
return !debugfs_create_file("rcuboost", 0444, rcudir, NULL,
&rcu_node_boost_fops);
}
#else /* #ifdef CONFIG_RCU_BOOST */
static int rcu_boost_trace_create_file(struct dentry *rcudir)
{
return 0; /* There cannot be an error if we didn't create it! */
}
#endif /* #else #ifdef CONFIG_RCU_BOOST */
static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
{
unsigned long gpnum;
int level = 0;
struct rcu_node *rnp;
gpnum = rsp->gpnum;
seq_printf(m, "c=%lu g=%lu s=%d jfq=%ld j=%x "
"nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu\n",
rsp->completed, gpnum, rsp->signaled,
(long)(rsp->jiffies_force_qs - jiffies),
(int)(jiffies & 0xffff),
rsp->n_force_qs, rsp->n_force_qs_ngp,
rsp->n_force_qs - rsp->n_force_qs_ngp,
rsp->n_force_qs_lh);
for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < NUM_RCU_NODES; rnp++) {
if (rnp->level != level) {
seq_puts(m, "\n");
level = rnp->level;
}
seq_printf(m, "%lx/%lx %c%c>%c %d:%d ^%d ",
rnp->qsmask, rnp->qsmaskinit,
".G"[rnp->gp_tasks != NULL],
".E"[rnp->exp_tasks != NULL],
".T"[!list_empty(&rnp->blkd_tasks)],
rnp->grplo, rnp->grphi, rnp->grpnum);
}
seq_puts(m, "\n");
}
static int show_rcuhier(struct seq_file *m, void *unused)
{
#ifdef CONFIG_TREE_PREEMPT_RCU
seq_puts(m, "rcu_preempt:\n");
print_one_rcu_state(m, &rcu_preempt_state);
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
seq_puts(m, "rcu_sched:\n");
print_one_rcu_state(m, &rcu_sched_state);
seq_puts(m, "rcu_bh:\n");
print_one_rcu_state(m, &rcu_bh_state);
return 0;
}
static int rcuhier_open(struct inode *inode, struct file *file)
{
return single_open(file, show_rcuhier, NULL);
}
static const struct file_operations rcuhier_fops = {
.owner = THIS_MODULE,
.open = rcuhier_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
static void show_one_rcugp(struct seq_file *m, struct rcu_state *rsp)
{
unsigned long flags;
unsigned long completed;
unsigned long gpnum;
unsigned long gpage;
unsigned long gpmax;
struct rcu_node *rnp = &rsp->node[0];
raw_spin_lock_irqsave(&rnp->lock, flags);
completed = rsp->completed;
gpnum = rsp->gpnum;
if (rsp->completed == rsp->gpnum)
gpage = 0;
else
gpage = jiffies - rsp->gp_start;
gpmax = rsp->gp_max;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
seq_printf(m, "%s: completed=%ld gpnum=%lu age=%ld max=%ld\n",
rsp->name, completed, gpnum, gpage, gpmax);
}
static int show_rcugp(struct seq_file *m, void *unused)
{
#ifdef CONFIG_TREE_PREEMPT_RCU
show_one_rcugp(m, &rcu_preempt_state);
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
show_one_rcugp(m, &rcu_sched_state);
show_one_rcugp(m, &rcu_bh_state);
return 0;
}
static int rcugp_open(struct inode *inode, struct file *file)
{
return single_open(file, show_rcugp, NULL);
}
static const struct file_operations rcugp_fops = {
.owner = THIS_MODULE,
.open = rcugp_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
static void print_one_rcu_pending(struct seq_file *m, struct rcu_data *rdp)
{
seq_printf(m, "%3d%cnp=%ld "
"qsp=%ld rpq=%ld cbr=%ld cng=%ld "
"gpc=%ld gps=%ld nf=%ld nn=%ld\n",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? '!' : ' ',
rdp->n_rcu_pending,
rdp->n_rp_qs_pending,
rdp->n_rp_report_qs,
rdp->n_rp_cb_ready,
rdp->n_rp_cpu_needs_gp,
rdp->n_rp_gp_completed,
rdp->n_rp_gp_started,
rdp->n_rp_need_fqs,
rdp->n_rp_need_nothing);
}
static void print_rcu_pendings(struct seq_file *m, struct rcu_state *rsp)
{
int cpu;
struct rcu_data *rdp;
for_each_possible_cpu(cpu) {
rdp = per_cpu_ptr(rsp->rda, cpu);
if (rdp->beenonline)
print_one_rcu_pending(m, rdp);
}
}
static int show_rcu_pending(struct seq_file *m, void *unused)
{
#ifdef CONFIG_TREE_PREEMPT_RCU
seq_puts(m, "rcu_preempt:\n");
print_rcu_pendings(m, &rcu_preempt_state);
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
seq_puts(m, "rcu_sched:\n");
print_rcu_pendings(m, &rcu_sched_state);
seq_puts(m, "rcu_bh:\n");
print_rcu_pendings(m, &rcu_bh_state);
return 0;
}
static int rcu_pending_open(struct inode *inode, struct file *file)
{
return single_open(file, show_rcu_pending, NULL);
}
static const struct file_operations rcu_pending_fops = {
.owner = THIS_MODULE,
.open = rcu_pending_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
static int show_rcutorture(struct seq_file *m, void *unused)
{
seq_printf(m, "rcutorture test sequence: %lu %s\n",
rcutorture_testseq >> 1,
(rcutorture_testseq & 0x1) ? "(test in progress)" : "");
seq_printf(m, "rcutorture update version number: %lu\n",
rcutorture_vernum);
return 0;
}
static int rcutorture_open(struct inode *inode, struct file *file)
{
return single_open(file, show_rcutorture, NULL);
}
static const struct file_operations rcutorture_fops = {
.owner = THIS_MODULE,
.open = rcutorture_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
static struct dentry *rcudir;
static int __init rcutree_trace_init(void)
{
struct dentry *retval;
rcudir = debugfs_create_dir("rcu", NULL);
if (!rcudir)
goto free_out;
retval = debugfs_create_file("rcudata", 0444, rcudir,
NULL, &rcudata_fops);
if (!retval)
goto free_out;
retval = debugfs_create_file("rcudata.csv", 0444, rcudir,
NULL, &rcudata_csv_fops);
if (!retval)
goto free_out;
if (rcu_boost_trace_create_file(rcudir))
goto free_out;
retval = debugfs_create_file("rcugp", 0444, rcudir, NULL, &rcugp_fops);
if (!retval)
goto free_out;
retval = debugfs_create_file("rcuhier", 0444, rcudir,
NULL, &rcuhier_fops);
if (!retval)
goto free_out;
retval = debugfs_create_file("rcu_pending", 0444, rcudir,
NULL, &rcu_pending_fops);
if (!retval)
goto free_out;
retval = debugfs_create_file("rcutorture", 0444, rcudir,
NULL, &rcutorture_fops);
if (!retval)
goto free_out;
return 0;
free_out:
debugfs_remove_recursive(rcudir);
return 1;
}
static void __exit rcutree_trace_cleanup(void)
{
debugfs_remove_recursive(rcudir);
}
module_init(rcutree_trace_init);
module_exit(rcutree_trace_cleanup);
MODULE_AUTHOR("Paul E. McKenney");
MODULE_DESCRIPTION("Read-Copy Update tracing for hierarchical implementation");
MODULE_LICENSE("GPL");
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