1/* SPDX-License-Identifier: GPL-2.0 */
  2/*
  3 * This program is free software; you can redistribute it and/or modify
  4 * it under the terms of the GNU General Public License as published by
  5 * the Free Software Foundation; either version 2 of the License, or
  6 * (at your option) any later version.
  7 *
  8 * This program is distributed in the hope that it will be useful,
  9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 11 * GNU General Public License for more details.
 12 *
 13 * Authors: Waiman Long <waiman.long@hpe.com>
 14 */
 15
 16/*
 17 * Collect locking event counts
 18 */
 19#include <linux/debugfs.h>
 20#include <linux/sched.h>
 21#include <linux/sched/clock.h>
 22#include <linux/fs.h>
 23
 24#include "lock_events.h"
 25
 26#undef  LOCK_EVENT
 27#define LOCK_EVENT(name)	[LOCKEVENT_ ## name] = #name,
 28
 29#define LOCK_EVENTS_DIR		"lock_event_counts"
 30
 31/*
 32 * When CONFIG_LOCK_EVENT_COUNTS is enabled, event counts of different
 33 * types of locks will be reported under the <debugfs>/lock_event_counts/
 34 * directory. See lock_events_list.h for the list of available locking
 35 * events.
 36 *
 37 * Writing to the special ".reset_counts" file will reset all the above
 38 * locking event counts. This is a very slow operation and so should not
 39 * be done frequently.
 40 *
 41 * These event counts are implemented as per-cpu variables which are
 42 * summed and computed whenever the corresponding debugfs files are read. This
 43 * minimizes added overhead making the counts usable even in a production
 44 * environment.
 45 */
 46static const char * const lockevent_names[lockevent_num + 1] = {
 47
 48#include "lock_events_list.h"
 49
 50	[LOCKEVENT_reset_cnts] = ".reset_counts",
 51};
 52
 53/*
 54 * Per-cpu counts
 55 */
 56DEFINE_PER_CPU(unsigned long, lockevents[lockevent_num]);
 57
 58/*
 59 * The lockevent_read() function can be overridden.
 60 */
 61ssize_t __weak lockevent_read(struct file *file, char __user *user_buf,
 62			      size_t count, loff_t *ppos)
 63{
 64	char buf[64];
 65	int cpu, id, len;
 66	u64 sum = 0;
 67
 68	/*
 69	 * Get the counter ID stored in file->f_inode->i_private
 70	 */
 71	id = (long)file_inode(file)->i_private;
 72
 73	if (id >= lockevent_num)
 74		return -EBADF;
 75
 76	for_each_possible_cpu(cpu)
 77		sum += per_cpu(lockevents[id], cpu);
 78	len = snprintf(buf, sizeof(buf) - 1, "%llu\n", sum);
 79
 80	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 81}
 82
 83/*
 84 * Function to handle write request
 85 *
 86 * When idx = reset_cnts, reset all the counts.
 87 */
 88static ssize_t lockevent_write(struct file *file, const char __user *user_buf,
 89			   size_t count, loff_t *ppos)
 90{
 91	int cpu;
 92
 93	/*
 94	 * Get the counter ID stored in file->f_inode->i_private
 95	 */
 96	if ((long)file_inode(file)->i_private != LOCKEVENT_reset_cnts)
 97		return count;
 98
 99	for_each_possible_cpu(cpu) {
100		int i;
101		unsigned long *ptr = per_cpu_ptr(lockevents, cpu);
102
103		for (i = 0 ; i < lockevent_num; i++)
104			WRITE_ONCE(ptr[i], 0);
105	}
106	return count;
107}
108
109/*
110 * Debugfs data structures
111 */
112static const struct file_operations fops_lockevent = {
113	.read = lockevent_read,
114	.write = lockevent_write,
115	.llseek = default_llseek,
116};
117
118#ifdef CONFIG_PARAVIRT_SPINLOCKS
119#include <asm/paravirt.h>
120
121static bool __init skip_lockevent(const char *name)
122{
123	static int pv_on __initdata = -1;
124
125	if (pv_on < 0)
126		pv_on = !pv_is_native_spin_unlock();
127	/*
128	 * Skip PV qspinlock events on bare metal.
129	 */
130	if (!pv_on && !memcmp(name, "pv_", 3))
131		return true;
132	return false;
133}
134#else
135static inline bool skip_lockevent(const char *name)
136{
137	return false;
138}
139#endif
140
141/*
142 * Initialize debugfs for the locking event counts.
143 */
144static int __init init_lockevent_counts(void)
145{
146	struct dentry *d_counts = debugfs_create_dir(LOCK_EVENTS_DIR, NULL);
147	int i;
148
149	if (!d_counts)
150		goto out;
151
152	/*
153	 * Create the debugfs files
154	 *
155	 * As reading from and writing to the stat files can be slow, only
156	 * root is allowed to do the read/write to limit impact to system
157	 * performance.
158	 */
159	for (i = 0; i < lockevent_num; i++) {
160		if (skip_lockevent(lockevent_names[i]))
161			continue;
162		if (!debugfs_create_file(lockevent_names[i], 0400, d_counts,
163					 (void *)(long)i, &fops_lockevent))
164			goto fail_undo;
165	}
166
167	if (!debugfs_create_file(lockevent_names[LOCKEVENT_reset_cnts], 0200,
168				 d_counts, (void *)(long)LOCKEVENT_reset_cnts,
169				 &fops_lockevent))
170		goto fail_undo;
171
172	return 0;
173fail_undo:
174	debugfs_remove_recursive(d_counts);
175out:
176	pr_warn("Could not create '%s' debugfs entries\n", LOCK_EVENTS_DIR);
177	return -ENOMEM;
178}
179fs_initcall(init_lockevent_counts);