1 files changed, 179 insertions, 0 deletions

diff --git a/kernel/locking/lock_events.c b/kernel/locking/lock_events.c
new file mode 100644
index 000000000000..fa2c2f951c6b
--- /dev/null
+++ b/kernel/locking/lock_events.c
@@ -0,0 +1,179 @@
+/* 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 (!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 (!debugfs_create_file(lockevent_names[i], 0400, d_counts,
+                                         (void *)(long)i, &fops_lockevent))
+                        goto fail_undo;
+        }
+
+        if (!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);