LXR linux/kernel/locking/lock

   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);
 180