/* SPDX-License-Identifier: GPL-2.0 */
/*
 * 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.
 *
 * Authors: Waiman Long <waiman.long@hpe.com>
 */

/*
 * Collect locking event counts
 */
#include <linux/debugfs.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/fs.h>

#include "lock_events.h"

#undef  LOCK_EVENT
#define LOCK_EVENT(name)        [LOCKEVENT_ ## name] = #name,

#define LOCK_EVENTS_DIR         "lock_event_counts"

/*
 * When CONFIG_LOCK_EVENT_COUNTS is enabled, event counts of different
 * types of locks will be reported under the <debugfs>/lock_event_counts/
 * directory. See lock_events_list.h for the list of available locking
 * events.
 *
 * Writing to the special ".reset_counts" file will reset all the above
 * locking event counts. This is a very slow operation and so should not
 * be done frequently.
 *
 * These event counts are implemented as per-cpu variables which are
 * summed and computed whenever the corresponding debugfs files are read. This
 * minimizes added overhead making the counts usable even in a production
 * environment.
 */
static const char * const lockevent_names[lockevent_num + 1] = {

#include "lock_events_list.h"

        [LOCKEVENT_reset_cnts] = ".reset_counts",
};

/*
 * Per-cpu counts
 */
DEFINE_PER_CPU(unsigned long, lockevents[lockevent_num]);

/*
 * The lockevent_read() function can be overridden.
 */
ssize_t __weak lockevent_read(struct file *file, char __user *user_buf,
                              size_t count, loff_t *ppos)
{
        char buf[64];
        int cpu, id, len;
        u64 sum = 0;

        /*
         * Get the counter ID stored in file->f_inode->i_private
         */
        id = (long)file_inode(file)->i_private;

        if (id >= lockevent_num)
                return -EBADF;

        for_each_possible_cpu(cpu)
                sum += per_cpu(lockevents[id], cpu);
        len = snprintf(buf, sizeof(buf) - 1, "%llu\n", sum);

        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}

/*
 * Function to handle write request
 *
 * When idx = reset_cnts, reset all the counts.
 */
static ssize_t lockevent_write(struct file *file, const char __user *user_buf,
                           size_t count, loff_t *ppos)
{
        int cpu;

        /*
         * Get the counter ID stored in file->f_inode->i_private
         */
        if ((long)file_inode(file)->i_private != LOCKEVENT_reset_cnts)
                return count;

        for_each_possible_cpu(cpu) {
                int i;
                unsigned long *ptr = per_cpu_ptr(lockevents, cpu);

                for (i = 0 ; i < lockevent_num; i++)
                        WRITE_ONCE(ptr[i], 0);
        }
        return count;
}

/*
 * Debugfs data structures
 */
static const struct file_operations fops_lockevent = {
        .read = lockevent_read,
        .write = lockevent_write,
        .llseek = default_llseek,
};

#ifdef CONFIG_PARAVIRT_SPINLOCKS
#include <asm/paravirt.h>

static bool __init skip_lockevent(const char *name)
{
        static int pv_on __initdata = -1;

        if (pv_on < 0)
                pv_on = !pv_is_native_spin_unlock();
        /*
         * Skip PV qspinlock events on bare metal.
         */
        if (!pv_on && !memcmp(name, "pv_", 3))
                return true;
        return false;
}
#else
static inline bool skip_lockevent(const char *name)
{
        return false;
}
#endif

/*
 * Initialize debugfs for the locking event counts.
 */
static int __init init_lockevent_counts(void)
{
        struct dentry *d_counts = debugfs_create_dir(LOCK_EVENTS_DIR, NULL);
        int i;

        if (IS_ERR(d_counts))
                goto out;

        /*
         * Create the debugfs files
         *
         * As reading from and writing to the stat files can be slow, only
         * root is allowed to do the read/write to limit impact to system
         * performance.
         */
        for (i = 0; i < lockevent_num; i++) {
                if (skip_lockevent(lockevent_names[i]))
                        continue;
                if (IS_ERR(debugfs_create_file(lockevent_names[i], 0400, d_counts,
                                         (void *)(long)i, &fops_lockevent)))
                        goto fail_undo;
        }

        if (IS_ERR(debugfs_create_file(lockevent_names[LOCKEVENT_reset_cnts], 0200,
                                 d_counts, (void *)(long)LOCKEVENT_reset_cnts,
                                 &fops_lockevent)))
                goto fail_undo;

        return 0;
fail_undo:
        debugfs_remove_recursive(d_counts);
out:
        pr_warn("Could not create '%s' debugfs entries\n", LOCK_EVENTS_DIR);
        return -ENOMEM;
}
fs_initcall(init_lockevent_counts);