marker.c

Kernel code of linux kernel

/*
 * Copyright (C) 2007 Mathieu Desnoyers
 *
 * 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.
 */
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/types.h>
#include <linux/jhash.h>
#include <linux/list.h>
#include <linux/rcupdate.h>
#include <linux/marker.h>
#include <linux/err.h>
#include <linux/slab.h>

extern struct marker __start___markers[];
extern struct marker __stop___markers[];

/* Set to 1 to enable marker debug output */
static const int marker_debug;

/*
 * markers_mutex nests inside module_mutex. Markers mutex protects the builtin
 * and module markers and the hash table.
 */
static DEFINE_MUTEX(markers_mutex);

/*
 * Marker hash table, containing the active markers.
 * Protected by module_mutex.
 */
#define MARKER_HASH_BITS 6
#define MARKER_TABLE_SIZE (1 << MARKER_HASH_BITS)

/*
 * Note about RCU :
 * It is used to make sure every handler has finished using its private data
 * between two consecutive operation (add or remove) on a given marker.  It is
 * also used to delay the free of multiple probes array until a quiescent state
 * is reached.
 * marker entries modifications are protected by the markers_mutex.
 */
struct marker_entry {
	struct hlist_node hlist;
	char *format;
			/* Probe wrapper */
	void (*call)(const struct marker *mdata, void *call_private, ...);
	struct marker_probe_closure single;
	struct marker_probe_closure *multi;
	int refcount;	/* Number of times armed. 0 if disarmed. */
	struct rcu_head rcu;
	void *oldptr;
	unsigned char rcu_pending:1;
	unsigned char ptype:1;
	char name[0];	/* Contains name'\0'format'\0' */
};

static struct hlist_head marker_table[MARKER_TABLE_SIZE];

/**
 * __mark_empty_function - Empty probe callback
 * @probe_private: probe private data
 * @call_private: call site private data
 * @fmt: format string
 * @...: variable argument list
 *
 * Empty callback provided as a probe to the markers. By providing this to a
 * disabled marker, we make sure the  execution flow is always valid even
 * though the function pointer change and the marker enabling are two distinct
 * operations that modifies the execution flow of preemptible code.
 */
void __mark_empty_function(void *probe_private, void *call_private,
	const char *fmt, va_list *args)
{
}
EXPORT_SYMBOL_GPL(__mark_empty_function);

/*
 * marker_probe_cb Callback that prepares the variable argument list for probes.
 * @mdata: pointer of type struct marker
 * @call_private: caller site private data
 * @...:  Variable argument list.
 *
 * Since we do not use "typical" pointer based RCU in the 1 argument case, we
 * need to put a full smp_rmb() in this branch. This is why we do not use
 * rcu_dereference() for the pointer read.
 */
void marker_probe_cb(const struct marker *mdata, void *call_private, ...)
{
	va_list args;
	char ptype;

	/*
	 * preempt_disable does two things : disabling preemption to make sure
	 * the teardown of the callbacks can be done correctly when they are in
	 * modules and they insure RCU read coherency.
	 */
	preempt_disable();
	ptype = mdata->ptype;
	if (likely(!ptype)) {
		marker_probe_func *func;
		/* Must read the ptype before ptr. They are not data dependant,
		 * so we put an explicit smp_rmb() here. */
		smp_rmb();
		func = mdata->single.func;
		/* Must read the ptr before private data. They are not data
		 * dependant, so we put an explicit smp_rmb() here. */
		smp_rmb();
		va_start(args, call_private);
		func(mdata->single.probe_private, call_private, mdata->format,
			&args);
		va_end(args);
	} else {
		struct marker_probe_closure *multi;
		int i;
		/*
		 * Read mdata->ptype before mdata->multi.
		 */
		smp_rmb();
		multi = mdata->multi;
		/*
		 * multi points to an array, therefore accessing the array
		 * depends on reading multi. However, even in this case,
		 * we must insure that the pointer is read _before_ the array
		 * data. Same as rcu_dereference, but we need a full smp_rmb()
		 * in the fast path, so put the explicit barrier here.
		 */
		smp_read_barrier_depends();
		for (i = 0; multi[i].func; i++) {
			va_start(args, call_private);
			multi[i].func(multi[i].probe_private, call_private,
				mdata->format, &args);
			va_end(args);
		}
	}
	preempt_enable();
}
EXPORT_SYMBOL_GPL(marker_probe_cb);

/*
 * marker_probe_cb Callback that does not prepare the variable argument list.
 * @mdata: pointer of type struct marker
 * @call_private: caller site private data
 * @...:  Variable argument list.
 *
 * Should be connected to markers "MARK_NOARGS".
 */
void marker_probe_cb_noarg(const struct marker *mdata, void *call_private, ...)
{
	va_list args;	/* not initialized */
	char ptype;

	preempt_disable();
	ptype = mdata->ptype;
	if (likely(!ptype)) {
		marker_probe_func *func;
		/* Must read the ptype before ptr. They are not data dependant,
		 * so we put an explicit smp_rmb() here. */
		smp_rmb();
		func = mdata->single.func;
		/* Must read the ptr before private data. They are not data
		 * dependant, so we put an explicit smp_rmb() here. */
		smp_rmb();
		func(mdata->single.probe_private, call_private, mdata->format,
			&args);
	} else {
		struct marker_probe_closure *multi;
		int i;
		/*
		 * Read mdata->ptype before mdata->multi.
		 */
		smp_rmb();
		multi = mdata->multi;
		/*
		 * multi points to an array, therefore accessing the array
		 * depends on reading multi. However, even in this case,
		 * we must insure that the pointer is read _before_ the array
		 * data. Same as rcu_dereference, but we need a full smp_rmb()
		 * in the fast path, so put the explicit barrier here.
		 */
		smp_read_barrier_depends();
		for (i = 0; multi[i].func; i++)
			multi[i].func(multi[i].probe_private, call_private,
				mdata->format, &args);
	}
	preempt_enable();
}
EXPORT_SYMBOL_GPL(marker_probe_cb_noarg);

static void free_old_closure(struct rcu_head *head)
{
	struct marker_entry *entry = container_of(head,
		struct marker_entry, rcu);
	kfree(entry->oldptr);
	/* Make sure we free the data before setting the pending flag to 0 */
	smp_wmb();
	entry->rcu_pending = 0;
}

static void debug_print_probes(struct marker_entry *entry)
{
	int i;

	if (!marker_debug)
		return;

	if (!entry->ptype) {
		printk(KERN_DEBUG "Single probe : %p %p\n",
			entry->single.func,
			entry->single.probe_private);
	} else {
		for (i = 0; entry->multi[i].func; i++)
			printk(KERN_DEBUG "Multi probe %d : %p %p\n", i,
				entry->multi[i].func,
				entry->multi[i].probe_private);
	}
}

static struct marker_probe_closure *
marker_entry_add_probe(struct marker_entry *entry,
		marker_probe_func *probe, void *probe_private)
{
	int nr_probes = 0;
	struct marker_probe_closure *old, *new;

	WARN_ON(!probe);

	debug_print_probes(entry);
	old = entry->multi;
	if (!entry->ptype) {
		if (entry->single.func == probe &&
				entry->single.probe_private == probe_private)
			return ERR_PTR(-EBUSY);
		if (entry->single.func == __mark_empty_function) {
			/* 0 -> 1 probes */
			entry->single.func = probe;
			entry->single.probe_private = probe_private;
			entry->refcount = 1;
			entry->ptype = 0;
			debug_print_probes(entry);
			return NULL;
		} else {
			/* 1 -> 2 probes */
			nr_probes = 1;
			old = NULL;
		}
	} else {
		/* (N -> N+1), (N != 0, 1) probes */
		for (nr_probes = 0; old[nr_probes].func; nr_probes++)
			if (old[nr_probes].func == probe
					&& old[nr_probes].probe_private
						== probe_private)
				return ERR_PTR(-EBUSY);
	}
	/* + 2 : one for new probe, one for NULL func */
	new = kzalloc((nr_probes + 2) * sizeof(struct marker_probe_closure),
			GFP_KERNEL);
	if (new == NULL)
		return ERR_PTR(-ENOMEM);
	if (!old)
		new[0] = entry->single;
	else
		memcpy(new, old,
			nr_probes * sizeof(struct marker_probe_closure));
	new[nr_probes].func = probe;
	new[nr_probes].probe_private = probe_private;
	entry->refcount = nr_probes + 1;
	entry->multi = new;
	entry->ptype = 1;
	debug_print_probes(entry);
	return old;
}

static struct marker_probe_closure *
marker_entry_remove_probe(struct marker_entry *entry,
		marker_probe_func *probe, void *probe_private)
{
	int nr_probes = 0, nr_del = 0, i;
	struct marker_probe_closure *old, *new;

	old = entry->multi;

	debug_print_probes(entry);
	if (!entry->ptype) {
		/* 0 -> N is an error */
		WARN_ON(entry->single.func == __mark_empty_function);
		/* 1 -> 0 probes */
		WARN_ON(probe && entry->single.func != probe);
		WARN_ON(entry->single.probe_private != probe_private);
		entry->single.func = __mark_empty_function;
		entry->refcount = 0;
		entry->ptype = 0;
		debug_print_probes(entry);
		return NULL;
	} else {
		/* (N -> M), (N > 1, M >= 0) probes */
		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
			if ((!probe || old[nr_probes].func == probe)
					&& old[nr_probes].probe_private
						== probe_private)
				nr_del++;
		}
	}

	if (nr_probes - nr_del == 0) {
		/* N -> 0, (N > 1) */
		entry->single.func = __mark_empty_function;
		entry->refcount = 0;
		entry->ptype = 0;
	} else if (nr_probes - nr_del == 1) {
		/* N -> 1, (N > 1) */
		for (i = 0; old[i].func; i++)
			if ((probe && old[i].func != probe) ||
					old[i].probe_private != probe_private)
				entry->single = old[i];
		entry->refcount = 1;
		entry->ptype = 0;
	} else {
		int j = 0;
		/* N -> M, (N > 1, M > 1) */
		/* + 1 for NULL */
		new = kzalloc((nr_probes - nr_del + 1)
			* sizeof(struct marker_probe_closure), GFP_KERNEL);
		if (new == NULL)
			return ERR_PTR(-ENOMEM);
		for (i = 0; old[i].func; i++)
			if ((probe && old[i].func != probe) ||
					old[i].probe_private != probe_private)
				new[j++] = old[i];
		entry->refcount = nr_probes - nr_del;
		entry->ptype = 1;
		entry->multi = new;
	}
	debug_print_probes(entry);
	return old;
}

/*
 * Get marker if the marker is present in the marker hash table.
 * Must be called with markers_mutex held.
 * Returns NULL if not present.
 */
static struct marker_entry *get_marker(const char *name)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct marker_entry *e;
	u32 hash = jhash(name, strlen(name), 0);

	head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name))
			return e;
	}
	return NULL;
}

/*
 * Add the marker to the marker hash table. Must be called with markers_mutex
 * held.
 */
static struct marker_entry *add_marker(const char *name, const char *format)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct marker_entry *e;
	size_t name_len = strlen(name) + 1;
	size_t format_len = 0;
	u32 hash = jhash(name, name_len-1, 0);

	if (format)
		format_len = strlen(format) + 1;
	head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name)) {
			printk(KERN_NOTICE
				"Marker %s busy\n", name);
			return ERR_PTR(-EBUSY);	/* Already there */
		}
	}
	/*
	 * Using kmalloc here to allocate a variable length element. Could
	 * cause some memory fragmentation if overused.
	 */
	e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
			GFP_KERNEL);
	if (!e)
		return ERR_PTR(-ENOMEM);
	memcpy(&e->name[0], name, name_len);
	if (format) {
		e->format = &e->name[name_len];
		memcpy(e->format, format, format_len);
		if (strcmp(e->format, MARK_NOARGS) == 0)
			e->call = marker_probe_cb_noarg;
		else
			e->call = marker_probe_cb;
		trace_mark(core_marker_format, "name %s format %s",
				e->name, e->format);
	} else {
		e->format = NULL;
		e->call = marker_probe_cb;
	}
	e->single.func = __mark_empty_function;
	e->single.probe_private = NULL;
	e->multi = NULL;
	e->ptype = 0;
	e->refcount = 0;
	e->rcu_pending = 0;
	hlist_add_head(&e->hlist, head);
	return e;
}

/*
 * Remove the marker from the marker hash table. Must be called with mutex_lock
 * held.
 */
static int remove_marker(const char *name)