[PATCH] lockdep: core

Do 'make oldconfig' and accept all the defaults for new config options -
reboot into the kernel and if everything goes well it should boot up fine and
you should have /proc/lockdep and /proc/lockdep_stats files.

Typically if the lock validator finds some problem it will print out
voluminous debug output that begins with "BUG: ..." and which syslog output
can be used by kernel developers to figure out the precise locking scenario.

What does the lock validator do?  It "observes" and maps all locking rules as
they occur dynamically (as triggered by the kernel's natural use of spinlocks,
rwlocks, mutexes and rwsems).  Whenever the lock validator subsystem detects a
new locking scenario, it validates this new rule against the existing set of
rules.  If this new rule is consistent with the existing set of rules then the
new rule is added transparently and the kernel continues as normal.  If the
new rule could create a deadlock scenario then this condition is printed out.

When determining validity of locking, all possible "deadlock scenarios" are
considered: assuming arbitrary number of CPUs, arbitrary irq context and task
context constellations, running arbitrary combinations of all the existing
locking scenarios.  In a typical system this means millions of separate
scenarios.  This is why we call it a "locking correctness" validator - for all
rules that are observed the lock validator proves it with mathematical
certainty that a deadlock could not occur (assuming that the lock validator
implementation itself is correct and its internal data structures are not
corrupted by some other kernel subsystem).  [see more details and conditionals
of this statement in include/linux/lockdep.h and
Documentation/lockdep-design.txt]

Furthermore, this "all possible scenarios" property of the validator also
enables the finding of complex, highly unlikely multi-CPU multi-context races
via single single-context rules, increasing the likelyhood of finding bugs
drastically.  In practical terms: the lock validator already found a bug in
the upstream kernel that could only occur on systems with 3 or more CPUs, and
which needed 3 very unlikely code sequences to occur at once on the 3 CPUs.
That bug was found and reported on a single-CPU system (!).  So in essence a
race will be found "piecemail-wise", triggering all the necessary components
for the race, without having to reproduce the race scenario itself!  In its
short existence the lock validator found and reported many bugs before they
actually caused a real deadlock.

To further increase the efficiency of the validator, the mapping is not per
"lock instance", but per "lock-class".  For example, all struct inode objects
in the kernel have inode->inotify_mutex.  If there are 10,000 inodes cached,
then there are 10,000 lock objects.  But ->inotify_mutex is a single "lock
type", and all locking activities that occur against ->inotify_mutex are
"unified" into this single lock-class.  The advantage of the lock-class
approach is that all historical ->inotify_mutex uses are mapped into a single
(and as narrow as possible) set of locking rules - regardless of how many
different tasks or inode structures it took to build this set of rules.  The
set of rules persist during the lifetime of the kernel.

To see the rough magnitude of checking that the lock validator does, here's a
portion of /proc/lockdep_stats, fresh after bootup:

 lock-classes:                            694 [max: 2048]
 direct dependencies:                  1598 [max: 8192]
 indirect dependencies:               17896
 all direct dependencies:             16206
 dependency chains:                    1910 [max: 8192]
 in-hardirq chains:                      17
 in-softirq chains:                     105
 in-process chains:                    1065
 stack-trace entries:                 38761 [max: 131072]
 combined max dependencies:         2033928
 hardirq-safe locks:                     24
 hardirq-unsafe locks:                  176
 softirq-safe locks:                     53
 softirq-unsafe locks:                  137
 irq-safe locks:                         59
 irq-unsafe locks:                      176

The lock validator has observed 1598 actual single-thread locking patterns,
and has validated all possible 2033928 distinct locking scenarios.

More details about the design of the lock validator can be found in
Documentation/lockdep-design.txt, which can also found at:

   http://redhat.com/~mingo/lockdep-patches/lockdep-design.txt

[bunk@stusta.de: cleanups]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

6 files changed, 2796 insertions, 0 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index e7fd20e70f1..049aa79e5c1 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -13,6 +13,7 @@ obj-y     = sched.o fork.o exec_domain.o panic.o printk.o profile.o \
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
 obj-y += time/
 obj-$(CONFIG_DEBUG_MUTEXES) += mutex-debug.o
+obj-$(CONFIG_LOCKDEP) += lockdep.o
 obj-$(CONFIG_FUTEX) += futex.o
 ifeq ($(CONFIG_COMPAT),y)
 obj-$(CONFIG_FUTEX) += futex_compat.o
diff --git a/kernel/fork.c b/kernel/fork.c
index b7db7fb74f5..7f48abdd7bb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1061,6 +1061,11 @@ static task_t *copy_process(unsigned long clone_flags,
 	p->hardirq_context = 0;
 	p->softirq_context = 0;
 #endif
+#ifdef CONFIG_LOCKDEP
+	p->lockdep_depth = 0; /* no locks held yet */
+	p->curr_chain_key = 0;
+	p->lockdep_recursion = 0;
+#endif
 
 	rt_mutex_init_task(p);
 
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index c911c6ec4dd..4e461438e48 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -410,6 +410,12 @@ int request_irq(unsigned int irq,
 	struct irqaction *action;
 	int retval;
 
+#ifdef CONFIG_LOCKDEP
+	/*
+	 * Lockdep wants atomic interrupt handlers:
+	 */
+	irqflags |= SA_INTERRUPT;
+#endif
 	/*
 	 * Sanity-check: shared interrupts must pass in a real dev-ID,
 	 * otherwise we'll have trouble later trying to figure out
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
new file mode 100644
index 00000000000..dd0580910a9
--- /dev/null
+++ b/kernel/lockdep.c
@@ -0,0 +1,2703 @@
+/*
+ * 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 <asm/sections.h>
+
+#include "lockdep_internals.h"
+
+/*
+ * hash_lock: protects the lockdep hashes and 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 hash_lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
+
+static int lockdep_initialized;
+
+unsigned long nr_list_entries;
+static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];
+
+/*
+ * Allocate a lockdep entry. (assumes hash_lock held, returns
+ * with NULL on failure)
+ */
+static struct lock_list *alloc_list_entry(void)
+{
+	if (nr_list_entries >= MAX_LOCKDEP_ENTRIES) {
+		__raw_spin_unlock(&hash_lock);
+		debug_locks_off();
+		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/2) ^ \
+	((key1) >> (64-MAX_LOCKDEP_KEYS_BITS/2)) ^ \
+	(key2))
+
+void lockdep_off(void)
+{
+	current->lockdep_recursion++;
+}
+
+EXPORT_SYMBOL(lockdep_off);
+
+void lockdep_on(void)
+{
+	current->lockdep_recursion--;
+}
+
+EXPORT_SYMBOL(lockdep_on);
+
+int lockdep_internal(void)
+{
+	return current->lockdep_recursion != 0;
+}
+
+EXPORT_SYMBOL(lockdep_internal);
+
+/*
+ * Debugging switches:
+ */
+
+#define VERBOSE			0
+#ifdef VERBOSE
+# define VERY_VERBOSE		0
+#endif
+
+#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:
+ */
+static int class_filter(struct lock_class *class)
+{
+	if (class->name_version == 1 &&
+			!strcmp(class->name, "&rl->lock"))
+		return 1;
+	if (class->name_version == 1 &&
+			!strcmp(class->name, "&ni->mrec_lock"))
+		return 1;
+	if (class->name_version == 1 &&
+			!strcmp(class->name, "mft_ni_runlist_lock"))
+		return 1;
+	if (class->name_version == 1 &&
+			!strcmp(class->name, "mft_ni_mrec_lock"))
+		return 1;
+	if (class->name_version == 1 &&
+			!strcmp(class->name, "&vol->lcnbmp_lock"))
+		return 1;
+	return 0;
+}
+#endif
+
+static int verbose(struct lock_class *class)
+{
+#if VERBOSE
+	return class_filter(class);
+#endif
+	return 0;
+}
+
+#ifdef CONFIG_TRACE_IRQFLAGS
+
+static int hardirq_verbose(struct lock_class *class)
+{
+#if HARDIRQ_VERBOSE
+	return class_filter(class);
+#endif
+	return 0;
+}
+
+static int softirq_verbose(struct lock_class *class)
+{
+#if SOFTIRQ_VERBOSE
+	return class_filter(class);
+#endif
+	return 0;
+}
+
+#endif
+
+/*
+ * Stack-trace: tightly packed array of stack backtrace
+ * addresses. Protected by the hash_lock.
+ */
+unsigned long nr_stack_trace_entries;
+static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES];
+
+static int save_trace(struct stack_trace *trace)
+{
+	trace->nr_entries = 0;
+	trace->max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
+	trace->entries = stack_trace + nr_stack_trace_entries;
+
+	save_stack_trace(trace, NULL, 0, 3);
+
+	trace->max_entries = trace->nr_entries;
+
+	nr_stack_trace_entries += trace->nr_entries;
+	if (DEBUG_LOCKS_WARN_ON(nr_stack_trace_entries > MAX_STACK_TRACE_ENTRIES))
+		return 0;
+
+	if (nr_stack_trace_entries == MAX_STACK_TRACE_ENTRIES) {
+		__raw_spin_unlock(&hash_lock);
+		if (debug_locks_off()) {
+			printk("BUG: MAX_STACK_TRACE_ENTRIES too low!\n");
+			printk("turning off the locking correctness validator.\n");
+			dump_stack();
+		}
+		return 0;
+	}
+
+	return 1;
+}
+
+unsigned int nr_hardirq_chains;
+unsigned int nr_softirq_chains;
+unsigned int nr_process_chains;
+unsigned int max_lockdep_depth;
+unsigned int max_recursion_depth;
+
+#ifdef CONFIG_DEBUG_LOCKDEP
+/*
+ * We cannot printk in early bootup code. Not even early_printk()
+ * might work. So we mark any initialization errors and printk
+ * about it later on, in lockdep_info().
+ */
+static int lockdep_init_error;
+
+/*
+ * Various lockdep statistics:
+ */
+atomic_t chain_lookup_hits;
+atomic_t chain_lookup_misses;
+atomic_t hardirqs_on_events;
+atomic_t hardirqs_off_events;
+atomic_t redundant_hardirqs_on;
+atomic_t redundant_hardirqs_off;
+atomic_t softirqs_on_events;
+atomic_t softirqs_off_events;
+atomic_t redundant_softirqs_on;
+atomic_t redundant_softirqs_off;
+atomic_t nr_unused_locks;
+atomic_t nr_cyclic_checks;
+atomic_t nr_cyclic_check_recursions;
+atomic_t nr_find_usage_forwards_checks;
+atomic_t nr_find_usage_forwards_recursions;
+atomic_t nr_find_usage_backwards_checks;
+atomic_t nr_find_usage_backwards_recursions;
+# define debug_atomic_inc(ptr)		atomic_inc(ptr)
+# define debug_atomic_dec(ptr)		atomic_dec(ptr)
+# define debug_atomic_read(ptr)		atomic_read(ptr)
+#else
+# define debug_atomic_inc(ptr)		do { } while (0)
+# define debug_atomic_dec(ptr)		do { } while (0)
+# define debug_atomic_read(ptr)		0
+#endif
+
+/*
+ * Locking printouts:
+ */
+
+static const char *usage_str[] =
+{
+	[LOCK_USED] =			"initial-use ",
+	[LOCK_USED_IN_HARDIRQ] =	"in-hardirq-W",
+	[LOCK_USED_IN_SOFTIRQ] =	"in-softirq-W",
+	[LOCK_ENABLED_SOFTIRQS] =	"softirq-on-W",
+	[LOCK_ENABLED_HARDIRQS] =	"hardirq-on-W",
+	[LOCK_USED_IN_HARDIRQ_READ] =	"in-hardirq-R",
+	[LOCK_USED_IN_SOFTIRQ_READ] =	"in-softirq-R",
+	[LOCK_ENABLED_SOFTIRQS_READ] =	"softirq-on-R",
+	[LOCK_ENABLED_HARDIRQS_READ] =	"hardirq-on-R",
+};
+
+const char * __get_key_name(struct lockdep_subclass_key *key, char *str)
+{
+	unsigned long offs, size;
+	char *modname;
+
+	return kallsyms_lookup((unsigned long)key, &size, &offs, &modname, str);
+}
+
+void
+get_usage_chars(struct lock_class *class, char *c1, char *c2, char *c3, char *c4)
+{
+	*c1 = '.', *c2 = '.', *c3 = '.', *c4 = '.';
+
+	if (class->usage_mask & LOCKF_USED_IN_HARDIRQ)
+		*c1 = '+';
+	else
+		if (class->usage_mask & LOCKF_ENABLED_HARDIRQS)
+			*c1 = '-';
+
+	if (class->usage_mask & LOCKF_USED_IN_SOFTIRQ)
+		*c2 = '+';
+	else
+		if (class->usage_mask & LOCKF_ENABLED_SOFTIRQS)
+			*c2 = '-';
+
+	if (class->usage_mask & LOCKF_ENABLED_HARDIRQS_READ)
+		*c3 = '-';
+	if (class->usage_mask & LOCKF_USED_IN_HARDIRQ_READ) {
+		*c3 = '+';
+		if (class->usage_mask & LOCKF_ENABLED_HARDIRQS_READ)
+			*c3 = '?';
+	}
+
+	if (class->usage_mask & LOCKF_ENABLED_SOFTIRQS_READ)
+		*c4 = '-';
+	if (class->usage_mask & LOCKF_USED_IN_SOFTIRQ_READ) {
+		*c4 = '+';
+		if (class->usage_mask & LOCKF_ENABLED_SOFTIRQS_READ)
+			*c4 = '?';
+	}
+}
+
+static void print_lock_name(struct lock_class *class)
+{
+	char str[128], c1, c2, c3, c4;
+	const char *name;
+
+	get_usage_chars(class, &c1, &c2, &c3, &c4);
+
+	name = class->name;
+	if (!name) {
+		name = __get_key_name(class->key, str);
+		printk(" (%s", name);
+	} else {
+		printk(" (%s", name);
+		if (class->name_version > 1)
+			printk("#%d", class->name_version);
+		if (class->subclass)
+			printk("/%d", class->subclass);
+	}
+	printk("){%c%c%c%c}", c1, c2, c3, c4);
+}
+
+static void print_lockdep_cache(struct lockdep_map *lock)
+{
+	const char *name;
+	char str[128];
+
+	name = lock->name;
+	if (!name)
+		name = __get_key_name(lock->key->subkeys, str);
+
+	printk("%s", name);
+}
+
+static void print_lock(struct held_lock *hlock)
+{
+	print_lock_name(hlock->class);
+	printk(", at: ");
+	print_ip_sym(hlock->acquire_ip);
+}
+
+static void lockdep_print_held_locks(struct task_struct *curr)
+{
+	int i, depth = curr->lockdep_depth;
+
+	if (!depth) {
+		printk("no locks held by %s/%d.\n", curr->comm, curr->pid);
+		return;
+	}
+	printk("%d lock%s held by %s/%d:\n",
+		depth, depth > 1 ? "s" : "", curr->comm, curr->pid);
+
+	for (i = 0; i < depth; i++) {
+		printk(" #%d: ", i);
+		print_lock(curr->held_locks + i);
+	}
+}
+/*
+ * Helper to print a nice hierarchy of lock dependencies:
+ */
+static void print_spaces(int nr)
+{
+	int i;
+
+	for (i = 0; i < nr; i++)
+		printk("  ");
+}
+
+static void print_lock_class_header(struct lock_class *class, int depth)
+{
+	int bit;
+
+	print_spaces(depth);
+	printk("->");
+	print_lock_name(class);
+	printk(" ops: %lu", class->ops);
+	printk(" {\n");
+
+	for (bit = 0; bit < LOCK_USAGE_STATES; bit++) {
+		if (class->usage_mask & (1 << bit)) {
+			int len = depth;
+
+			print_spaces(depth);
+			len += printk("   %s", usage_str[bit]);
+			len += printk(" at:\n");
+			print_stack_trace(class->usage_traces + bit, len);
+		}
+	}
+	print_spaces(depth);
+	printk(" }\n");
+
+	print_spaces(depth);
+	printk(" ... key      at: ");
+	print_ip_sym((unsigned long)class->key);
+}
+
+/*
+ * printk all lock dependencies starting at <entry>:
+ */
+static void print_lock_dependencies(struct lock_class *class, int depth)
+{
+	struct lock_list *entry;
+
+	if (DEBUG_LOCKS_WARN_ON(depth >= 20))
+		return;
+
+	print_lock_class_header(class, depth);
+
+	list_for_each_entry(entry, &class->locks_after, entry) {
+		DEBUG_LOCKS_WARN_ON(!entry->class);
+		print_lock_dependencies(entry->class, depth + 1);
+
+		print_spaces(depth);
+		printk(" ... acquired at:\n");
+		print_stack_trace(&entry->trace, 2);
+		printk("\n");
+	}
+}
+
+/*
+ * Add a new dependency to the head of the list:
+ */
+static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
+			    struct list_head *head, unsigned long ip)
+{
+	struct lock_list *entry;
+	/*
+	 * Lock not present yet - get a new dependency struct and
+	 * add it to the list:
+	 */
+	entry = alloc_list_entry();
+	if (!entry)
+		return 0;
+
+	entry->class = this;
+	save_trace(&entry->trace);
+
+	/*
+	 * Since we never remove from the dependency list, the list can
+	 * be walked lockless by other CPUs, it's only allocation
+	 * that must be protected by the spinlock. But this also means
+	 * we must make new entries visible only once writes to the
+	 * entry become visible - hence the RCU op:
+	 */
+	list_add_tail_rcu(&entry->entry, head);
+
+	return 1;
+}
+
+/*
+ * Recursive, forwards-direction lock-dependency checking, used for
+ * both noncyclic checking and for hardirq-unsafe/softirq-unsafe
+ * checking.
+ *
+ * (to keep the stackframe of the recursive functions small we
+ *  use these global variables, and we also mark various helper
+ *  functions as noinline.)
+ */
+static struct held_lock *check_source, *check_target;
+
+/*
+ * Print a dependency chain entry (this is only done when a deadlock
+ * has been detected):
+ */
+static noinline int
+print_circular_bug_entry(struct lock_list *target, unsigned int depth)
+{
+	if (debug_locks_silent)
+		return 0;
+	printk("\n-> #%u", depth);
+	print_lock_name(target->class);
+	printk(":\n");
+	print_stack_trace(&target->trace, 6);
+
+	return 0;
+}
+
+/*
+ * When a circular dependency is detected, print the
+ * header first:
+ */
+static noinline int
+print_circular_bug_header(struct lock_list *entry, unsigned int depth)
+{
+	struct task_struct *curr = current;
+
+	__raw_spin_unlock(&hash_lock);
+	debug_locks_off();
+	if (debug_locks_silent)
+		return 0;
+
+	printk("\n=======================================================\n");
+	printk(  "[ INFO: possible circular locking dependency detected ]\n");
+	printk(  "-------------------------------------------------------\n");
+	printk("%s/%d is trying to acquire lock:\n",
+		curr->comm, curr->pid);
+	print_lock(check_source);
+	printk("\nbut task is already holding lock:\n");
+	print_lock(check_target);
+	printk("\nwhich lock already depends on the new lock.\n\n");
+	printk("\nthe existing dependency chain (in reverse order) is:\n");
+
+	print_circular_bug_entry(entry, depth);
+
+	return 0;
+}
+
+static noinline int print_circular_bug_tail(void)
+{
+	struct task_struct *curr = current;
+	struct lock_list this;
+
+	if (debug_locks_silent)
+		return 0;
+
+	this.class = check_source->class;
+	save_trace(&this.trace);
+	print_circular_bug_entry(&this, 0);
+
+	printk("\nother info that might help us debug this:\n\n");
+	lockdep_print_held_locks(curr);
+
+	printk("\nstack backtrace:\n");
+	dump_stack();
+
+	return 0;
+}
+
+static int noinline print_infinite_recursion_bug(void)
+{
+	__raw_spin_unlock(&hash_lock);
+	DEBUG_LOCKS_WARN_ON(1);
+
+	return 0;
+}
+
+/*
+ * Prove that the dependency graph starting at <entry> can not
+ * lead to <target>. Print an error and return 0 if it does.
+ */
+static noinline int
+check_noncircular(struct lock_class *source, unsigned int depth)
+{
+	struct lock_list *entry;
+
+	debug_atomic_inc(&nr_cyclic_check_recursions);
+	if (depth > max_recursion_depth)
+		max_recursion_depth = depth;
+	if (depth >= 20)
+		return print_infinite_recursion_bug();
+	/*
+	 * Check this lock's dependency list:
+	 */
+	list_for_each_entry(entry, &source->locks_after, entry) {
+		if (entry->class == check_target->class)
+			return print_circular_bug_header(entry, depth+1);
+		debug_atomic_inc(&nr_cyclic_checks);
+		if (!check_noncircular(entry->class, depth+1))
+			return print_circular_bug_entry(entry, depth+1);
+	}
+	return 1;
+}
+
+static int very_verbose(struct lock_class *class)
+{
+#if VERY_VERBOSE
+	return class_filter(class);
+#endif
+	return 0;
+}
+#ifdef CONFIG_TRACE_IRQFLAGS
+
+/*
+ * Forwards and backwards subgraph searching, for the purposes of
+ * proving that two subgraphs can be connected by a new dependency
+ * without creating any illegal irq-safe -> irq-unsafe lock dependency.
+ */
+static enum lock_usage_bit find_usage_bit;
+static struct lock_class *forwards_match, *backwards_match;
+
+/*
+ * Find a node in the forwards-direction dependency sub-graph starting
+ * at <source> that matches <find_usage_bit>.
+ *
+ * Return 2 if such a node exists in the subgraph, and put that node
+ * into <forwards_match>.
+ *
+ * Return 1 otherwise and keep <forwards_match> unchanged.
+ * Return 0 on error.
+ */
+static noinline int
+find_usage_forwards(struct lock_class *source, unsigned int depth)
+{
+	struct lock_list *entry;
+	int ret;
+
+	if (depth > max_recursion_depth)
+		max_recursion_depth = depth;
+	if (depth >= 20)
+		return print_infinite_recursion_bug();
+
+	debug_atomic_inc(&nr_find_usage_forwards_checks);
+	if (source->usage_mask & (1 << find_usage_bit)) {
+		forwards_match = source;
+		return 2;
+	}
+
+	/*
+	 * Check this lock's dependency list:
+	 */
+	list_for_each_entry(entry, &source->locks_after, entry) {
+		debug_atomic_inc(&nr_find_usage_forwards_recursions);
+		ret = find_usage_forwards(entry->class, depth+1);
+		if (ret == 2 || ret == 0)
+			return ret;
+	}
+	return 1;
+}
+
+/*
+ * Find a node in the backwards-direction dependency sub-graph starting
+ * at <source> that matches <find_usage_bit>.
+ *
+ * Return 2 if such a node exists in the subgraph, and put that node
+ * into <backwards_match>.
+ *
+ * Return 1 otherwise and keep <backwards_match> unchanged.
+ * Return 0 on error.
+ */
+static noinline int
+find_usage_backwards(struct lock_class *source, unsigned int depth)
+{
+	struct lock_list *entry;
+	int ret;
+
+	if (depth > max_recursion_depth)
+		max_recursion_depth = depth;
+	if (depth >= 20)
+		return print_infinite_recursion_bug();
+
+	debug_atomic_inc(&nr_find_usage_backwards_checks);
+	if (source->usage_mask & (1 << find_usage_bit)) {
+		backwards_match = source;
+		return 2;
+	}
+
+	/*
+	 * Check this lock's dependency list:
+	 */
+	list_for_each_entry(entry, &source->locks_before, entry) {
+		debug_atomic_inc(&nr_find_usage_backwards_recursions);
+		ret = find_usage_backwards(entry->class, depth+1);
+		if (ret == 2 || ret == 0)
+			return ret;
+	}
+	return 1;
+}
+
+static int
+print_bad_irq_dependency(struct task_struct *curr,
+			 struct held_lock *prev,
+			 struct held_lock *next,
+			 enum lock_usage_bit bit1,
+			 enum lock_usage_bit bit2,
+			 const char *irqclass)
+{
+	__raw_spin_unlock(&hash_lock);
+	debug_locks_off();
+	if (debug_locks_silent)
+		return 0;
+
+	printk("\n======================================================\n");
+	printk(  "[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
+		irqclass, irqclass);
+	printk(  "------------------------------------------------------\n");
+	printk("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] is trying to acquire:\n",
+		curr->comm, curr->pid,
+		curr->hardirq_context, hardirq_count() >> HARDIRQ_SHIFT,
+		curr->softirq_context, softirq_count() >> SOFTIRQ_SHIFT,
+		curr->hardirqs_enabled,
+		curr->softirqs_enabled);
+	print_lock(next);
+
+	printk("\nand this task is already holding:\n");
+	print_lock(prev);
+	printk("which would create a new lock dependency:\n");
+	print_lock_name(prev->class);
+	printk(" ->");
+	print_lock_name(next->class);
+	printk("\n");
+
+	printk("\nbut this new dependency connects a %s-irq-safe lock:\n",
+		irqclass);
+	print_lock_name(backwards_match);
+	printk("\n... which became %s-irq-safe at:\n", irqclass);
+
+	print_stack_trace(backwards_match->usage_traces + bit1, 1);
+
+	printk("\nto a %s-irq-unsafe lock:\n", irqclass);
+	print_lock_name(forwards_match);
+	printk("\n... which became %s-irq-unsafe at:\n", irqclass);
+	printk("...");
+
+	print_stack_trace(forwards_match->usage_traces + bit2, 1);
+
+	printk("\nother info that might help us debug this:\n\n");
+	lockdep_print_held_locks(curr);
+
+	printk("\nthe %s-irq-safe lock's dependencies:\n", irqclass);
+	print_lock_dependencies(backwards_match, 0);
+
+	printk("\nthe %s-irq-unsafe lock's dependencies:\n", irqclass);
+	print_lock_dependencies(forwards_match, 0);
+
+	printk("\nstack backtrace:\n");
+	dump_stack();
+
+	return 0;
+}
+
+static int
+check_usage(struct task_struct *curr, struct held_lock *prev,
+	    struct held_lock *next, enum lock_usage_bit bit_backwards,
+	    enum lock_usage_bit bit_forwards, const char *irqclass)
+{
+	int ret;
+
+	find_usage_bit = bit_backwards;
+	/* fills in <backwards_match> */
+	ret = find_usage_backwards(prev->class, 0);
+	if (!ret || ret == 1)
+		return ret;
+
+	find_usage_bit = bit_forwards;
+	ret = find_usage_forwards(next->class, 0);
+	if (!ret || ret == 1)
+		return ret;
+	/* ret == 2 */
+	return print_bad_irq_dependency(curr, prev, next,
+			bit_backwards, bit_forwards, irqclass);
+}
+
+#endif
+
+static int
+print_deadlock_bug(struct task_struct *curr, struct held_lock *prev,
+		   struct held_lock *next)
+{
+	debug_locks_off();
+	__raw_spin_unlock(&hash_lock);
+	if (debug_locks_silent)
+		return 0;
+
+	printk("\n=============================================\n");
+	printk(  "[ INFO: possible recursive locking detected ]\n");
+	printk(  "---------------------------------------------\n");
+	printk("%s/%d is trying to acquire lock:\n",
+		curr->comm, curr->pid);
+	print_lock(next);
+	printk("\nbut task is already holding lock:\n");
+	print_lock(prev);
+
+	printk("\nother info that might help us debug this:\n");
+	lockdep_print_held_locks(curr);
+
+	printk("\nstack backtrace:\n");
+	dump_stack();
+
+	return 0;
+}
+
+/*
+ * Check whether we are holding such a class already.
+ *
+ * (Note that this has to be done separately, because the graph cannot
+ * detect such classes of deadlocks.)
+ *
+ * Returns: 0 on deadlock detected, 1 on OK, 2 on recursive read
+ */
+static int
+check_deadlock(struct task_struct *curr, struct held_lock *next,
+	       struct lockdep_map *next_instance, int read)
+{
+	struct held_lock *prev;
+	int i;
+
+	for (i = 0; i < curr->lockdep_depth; i++) {
+		prev = curr->held_locks + i;
+		if (prev->class != next->class)
+			continue;
+		/*
+		 * Allow read-after-read recursion of the same
+		 * lock instance (i.e. read_lock(lock)+read_lock(lock)):
+		 */
+		if ((read == 2) && prev->read &&
+				(prev->instance == next_instance))
+			return 2;
+		return print_deadlock_bug(curr, prev, next);
+	}
+	return 1;
+}
+
+/*
+ * There was a chain-cache miss, and we are about to add a new dependency
+ * to a previous lock. We recursively validate the following rules:
+ *
+ *  - would the adding of the <prev> -> <next> dependency create a
+ *    circular dependency in the graph? [== circular deadlock]
+ *
+ *  - does the new prev->next dependency connect any hardirq-safe lock
+ *    (in the full backwards-subgraph starting at <prev>) with any
+ *    hardirq-unsafe lock (in the full forwards-subgraph starting at
+ *    <next>)? [== illegal lock inversion with hardirq contexts]
+ *
+ *  - does the new prev->next dependency connect any softirq-safe lock
+ *    (in the full backwards-subgraph starting at <prev>) with any
+ *    softirq-unsafe lock (in the full forwards-subgraph starting at
+ *    <next>)? [== illegal lock inversion with softirq contexts]
+ *
+ * any of these scenarios could lead to a deadlock.
+ *
+ * Then if all the validations pass, we add the forwards and backwards
+ * dependency.
+ */
+static int
+check_prev_add(struct task_struct *curr, struct held_lock *prev,
+	       struct held_lock *next)
+{
+	struct lock_list *entry;
+	int ret;
+
+	/*
+	 * Prove that the new <prev> -> <next> dependency would not
+	 * create a circular dependency in the graph. (We do this by
+	 * forward-recursing into the graph starting at <next>, and
+	 * checking whether we can reach <prev>.)
+	 *
+	 * We are using global variables to control the recursion, to
+	 * keep the stackframe size of the recursive functions low:
+	 */
+	check_source = next;
+	check_target = prev;
+	if (!(check_noncircular(next->class, 0)))
+		return print_circular_bug_tail();
+
+#ifdef CONFIG_TRACE_IRQFLAGS
+	/*
+	 * Prove that the new dependency does not connect a hardirq-safe
+	 * lock with a hardirq-unsafe lock - to achieve this we search
+	 * the backwards-subgraph starting at <prev>, and the
+	 * forwards-subgraph starting at <next>:
+	 */
+	if (!check_usage(curr, prev, next, LOCK_USED_IN_HARDIRQ,
+					LOCK_ENABLED_HARDIRQS, "hard"))
+		return 0;
+
+	/*
+	 * Prove that the new dependency does not connect a hardirq-safe-read
+	 * lock with a hardirq-unsafe lock - to achieve this we search
+	 * the backwards-subgraph starting at <prev>, and the
+	 * forwards-subgraph starting at <next>:
+	 */
+	if (!check_usage(curr, prev, next, LOCK_USED_IN_HARDIRQ_READ,
+					LOCK_ENABLED_HARDIRQS, "hard-read"))
+		return 0;
+
+	/*
+	 * Prove that the new dependency does not connect a softirq-safe
+	 * lock with a softirq-unsafe lock - to achieve this we search
+	 * the backwards-subgraph starting at <prev>, and the
+	 * forwards-subgraph starting at <next>:
+	 */
+	if (!check_usage(curr, prev, next, LOCK_USED_IN_SOFTIRQ,
+					LOCK_ENABLED_SOFTIRQS, "soft"))
+		return 0;
+	/*
+	 * Prove that the new dependency does not connect a softirq-safe-read
+	 * lock with a softirq-unsafe lock - to achieve this we search
+	 * the backwards-subgraph starting at <prev>, and the
+	 * forwards-subgraph starting at <next>:
+	 */
+	if (!check_usage(curr, prev, next, LOCK_USED_IN_SOFTIRQ_READ,
+					LOCK_ENABLED_SOFTIRQS, "soft"))
+		return 0;
+#endif
+	/*
+	 * For recursive read-locks we do all the dependency checks,
+	 * but we dont store read-triggered dependencies (only
+	 * write-triggered dependencies). This ensures that only the
+	 * write-side dependencies matter, and that if for example a
+	 * write-lock never takes any other locks, then the reads are
+	 * equivalent to a NOP.
+	 */
+	if (next->read == 2 || prev->read == 2)
+		return 1;
+	/*
+	 * Is the <prev> -> <next> dependency already present?
+	 *
+	 * (this may occur even though this is a new chain: consider
+	 *  e.g. the L1 -> L2 -> L3 -> L4 and the L5 -> L1 -> L2 -> L3
+	 *  chains - the second one will be new, but L1 already has
+	 *  L2 added to its dependency list, due to the first chain.)
+	 */
+	list_for_each_entry(entry, &prev->class->locks_after, entry) {
+		if (entry->class == next->class)
+			return 2;
+	}
+
+	/*
+	 * Ok, all validations passed, add the new lock
+	 * to the previous lock's dependency list:
+	 */
+	ret = add_lock_to_list(prev->class, next->class,
+			       &prev->class->locks_after, next->acquire_ip);
+	if (!ret)
+		return 0;
+	/*
+	 * Return value of 2 signals 'dependency already added',
+	 * in that case we dont have to add the backlink either.
+	 */
+	if (ret == 2)
+		return 2;
+