lockdep.c

/*
 * kernel/lockdep.c
 *
 * Runtime locking correctness validator
 *
 * Started by Ingo Molnar:
 *
 *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 * this code maps all the lock dependencies as they occur in a live kernel
 * and will warn about the following classes of locking bugs:
 *
 * - lock inversion scenarios
 * - circular lock dependencies
 * - hardirq/softirq safe/unsafe locking bugs
 *
 * Bugs are reported even if the current locking scenario does not cause
 * any deadlock at this point.
 *
 * I.e. if anytime in the past two locks were taken in a different order,
 * even if it happened for another task, even if those were different
 * locks (but of the same class as this lock), this code will detect it.
 *
 * Thanks to Arjan van de Ven for coming up with the initial idea of
 * mapping lock dependencies runtime.
 */
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/spinlock.h>
#include <linux/kallsyms.h>
#include <linux/interrupt.h>
#include <linux/stacktrace.h>
#include <linux/debug_locks.h>
#include <linux/irqflags.h>
#include <linux/utsname.h>

#include <asm/sections.h>

#include "lockdep_internals.h"

/*
 * lockdep_lock: protects the lockdep graph, the hashes and the
 *               class/list/hash allocators.
 *
 * This is one of the rare exceptions where it's justified
 * to use a raw spinlock - we really dont want the spinlock
 * code to recurse back into the lockdep code...
 */
static raw_spinlock_t lockdep_lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;

static int graph_lock(void)
{
	__raw_spin_lock(&lockdep_lock);
	/*
	 * Make sure that if another CPU detected a bug while
	 * walking the graph we dont change it (while the other
	 * CPU is busy printing out stuff with the graph lock
	 * dropped already)
	 */
	if (!debug_locks) {
		__raw_spin_unlock(&lockdep_lock);
		return 0;
	}
	return 1;
}

static inline int graph_unlock(void)
{
	if (debug_locks && !__raw_spin_is_locked(&lockdep_lock))
		return DEBUG_LOCKS_WARN_ON(1);

	__raw_spin_unlock(&lockdep_lock);
	return 0;
}

/*
 * Turn lock debugging off and return with 0 if it was off already,
 * and also release the graph lock:
 */
static inline int debug_locks_off_graph_unlock(void)
{
	int ret = debug_locks_off();

	__raw_spin_unlock(&lockdep_lock);

	return ret;
}

static int lockdep_initialized;

unsigned long nr_list_entries;
static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];

/*
 * Allocate a lockdep entry. (assumes the graph_lock held, returns
 * with NULL on failure)
 */
static struct lock_list *alloc_list_entry(void)
{
	if (nr_list_entries >= MAX_LOCKDEP_ENTRIES) {
		if (!debug_locks_off_graph_unlock())
			return NULL;

		printk("BUG: MAX_LOCKDEP_ENTRIES too low!\n");
		printk("turning off the locking correctness validator.\n");
		return NULL;
	}
	return list_entries + nr_list_entries++;
}

/*
 * All data structures here are protected by the global debug_lock.
 *
 * Mutex key structs only get allocated, once during bootup, and never
 * get freed - this significantly simplifies the debugging code.
 */
unsigned long nr_lock_classes;
static struct lock_class lock_classes[MAX_LOCKDEP_KEYS];

/*
 * We keep a global list of all lock classes. The list only grows,
 * never shrinks. The list is only accessed with the lockdep
 * spinlock lock held.
 */
LIST_HEAD(all_lock_classes);

/*
 * The lockdep classes are in a hash-table as well, for fast lookup:
 */
#define CLASSHASH_BITS		(MAX_LOCKDEP_KEYS_BITS - 1)
#define CLASSHASH_SIZE		(1UL << CLASSHASH_BITS)
#define CLASSHASH_MASK		(CLASSHASH_SIZE - 1)
#define __classhashfn(key)	((((unsigned long)key >> CLASSHASH_BITS) + (unsigned long)key) & CLASSHASH_MASK)
#define classhashentry(key)	(classhash_table + __classhashfn((key)))

static struct list_head classhash_table[CLASSHASH_SIZE];

unsigned long nr_lock_chains;
static struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];

/*
 * We put the lock dependency chains into a hash-table as well, to cache
 * their existence:
 */
#define CHAINHASH_BITS		(MAX_LOCKDEP_CHAINS_BITS-1)
#define CHAINHASH_SIZE		(1UL << CHAINHASH_BITS)
#define CHAINHASH_MASK		(CHAINHASH_SIZE - 1)
#define __chainhashfn(chain) \
		(((chain >> CHAINHASH_BITS) + chain) & CHAINHASH_MASK)
#define chainhashentry(chain)	(chainhash_table + __chainhashfn((chain)))

static struct list_head chainhash_table[CHAINHASH_SIZE];

/*
 * The hash key of the lock dependency chains is a hash itself too:
 * it's a hash of all locks taken up to that lock, including that lock.
 * It's a 64-bit hash, because it's important for the keys to be
 * unique.
 */
#define iterate_chain_key(key1, key2) \
	(((key1) << MAX_LOCKDEP_KEYS_BITS) ^ \
	((key1) >> (64-MAX_LOCKDEP_KEYS_BITS)) ^ \
	(key2))

void lockdep_off(void)
{
	current->lockdep_recursion++;
}

EXPORT_SYMBOL(lockdep_off);

void lockdep_on(void)
{
	current->lockdep_recursion--;
}

EXPORT_SYMBOL(lockdep_on);

/*
 * Debugging switches:
 */

#define VERBOSE			0
#define VERY_VERBOSE		0

#if VERBOSE
# define HARDIRQ_VERBOSE	1
# define SOFTIRQ_VERBOSE	1
#else
# define HARDIRQ_VERBOSE	0
# define SOFTIRQ_VERBOSE	0
#endif

#if VERBOSE || HARDIRQ_VERBOSE || SOFTIRQ_VERBOSE
/*
 * Quick filtering for interesting events: