Date:	Sun, 20 May 2007 12:30:26 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-kernel@...r.kernel.org
Cc:	Jason Baron <jbaron@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Bill Huey <billh@...ppy.monkey.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: [PATCH] lockdep: lock contention tracking


Add lock contention tracking to lockdep

[root@...jtu ~]# cat /proc/lockdep_contentions | sort -rnk 2 | head
dcache_lock: 3000 0 [618] [<ffffffff8033badd>] _atomic_dec_and_lock+0x39/0x58 [17] [<ffffffff802d6dce>] sysfs_open_file+0x28/0x25a [160] [<ffffffff802a5b61>] d_instantiate+0x2a/0xad [52] [<ffffffff8029d926>] __link_path_walk+0x270/0xde9
&inode->i_mutex: 235 0 [15] [<ffffffff8029b053>] pipe_read+0x74/0x39d [23] [<ffffffff8029a9f8>] pipe_wait+0x86/0x8d [105] [<ffffffff8029bc9a>] do_lookup+0x81/0x1ae [85] [<ffffffff802a0be7>] vfs_readdir+0x5c/0xa9
&zone->lru_lock: 141 0 [11] [<ffffffff8027366b>] activate_page+0x37/0xd6 [75] [<ffffffff80273327>] release_pages+0xb2/0x16c [42] [<ffffffff80273443>] __pagevec_lru_add_active+0x62/0xe5 [12] [<ffffffff80273529>] __pagevec_lru_add+0x63/0xe2
&rq->rq_lock_key: 93 0 [66] [<ffffffff8022b202>] task_rq_lock+0x42/0x74 [24] [<ffffffff80461f2a>] __sched_text_start+0x17a/0x869 [2] [<ffffffff8022a58e>] double_rq_lock+0x38/0x3d [1] [<ffffffff8022b1af>] double_lock_balance+0x41/0x52
&rq->rq_lock_key: 59 0 [15] [<ffffffff80461f2a>] __sched_text_start+0x17a/0x869 [27] [<ffffffff8022b202>] task_rq_lock+0x42/0x74 [17] [<ffffffff80462090>] __sched_text_start+0x2e0/0x869
files_lock: 57 0 [28] [<ffffffff8029581d>] file_move+0x1d/0x51 [29] [<ffffffff802957dc>] file_kill+0x15/0x39
&inode->i_data.i_mmap_lock: 52 0 [16] [<ffffffff8023149f>] copy_process+0xe10/0x1684 [5] [<ffffffff8027e38d>] vma_link+0x40/0x107 [20] [<ffffffff8027d866>] unlink_file_vma+0x2c/0x53 [11] [<ffffffff8027da53>] vma_adjust+0x154/0x452
&q->__queue_lock: 47 0 [16] [<ffffffff8033348a>] __make_request+0x5e/0x663 [4] [<ffffffff803339e8>] __make_request+0x5bc/0x663 [2] [<ffffffff803320c3>] generic_unplug_device+0x18/0x25 [1] [<ffffffff803320bb>] generic_unplug_device+0x10/0x25
&dentry->d_lock: 26 0 [22] [<ffffffff802a58be>] __d_lookup+0x7d/0x136 [4] [<ffffffff802ccd61>] dnotify_parent+0x1f/0x6d
vfsmount_lock: 17 0 [16] [<ffffffff802ab31d>] lookup_mnt+0x19/0x4c [1] [<ffffffff802a51df>] __d_path+0xae/0x14c

read as:
<lock name> <(write) contentiond> <read contentions>
 (<contentions> <ip> <symbol>){,4}

The 4 points are the first 4 unique callsites that cause lock contention
for the specified lock class.

writing a 0 to /proc/lockdep_contentions clears the stats

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 include/linux/lockdep.h |   14 +++++++
 kernel/lockdep.c        |   96 ++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/lockdep_proc.c   |   77 ++++++++++++++++++++++++++++++++++++++
 kernel/mutex.c          |    7 +++
 kernel/rwsem.c          |   20 ++++++++--
 kernel/spinlock.c       |   70 ++++++++++++++++++++++++++++-------
 6 files changed, 266 insertions(+), 18 deletions(-)

Index: linux-2.6/include/linux/lockdep.h
===================================================================
--- linux-2.6.orig/include/linux/lockdep.h	2007-04-03 13:58:27.000000000 +0200
+++ linux-2.6/include/linux/lockdep.h	2007-05-19 10:26:44.000000000 +0200
@@ -16,6 +16,7 @@ struct task_struct;
 #include <linux/list.h>
 #include <linux/debug_locks.h>
 #include <linux/stacktrace.h>
+#include <asm/atomic.h>
 
 /*
  * Lock-class usage-state bits:
@@ -71,6 +72,11 @@ struct lock_class_key {
 	struct lockdep_subclass_key	subkeys[MAX_LOCKDEP_SUBCLASSES];
 };
 
+struct lockdep_contention_point {
+	unsigned long ip;
+	atomic_t count;
+};
+
 /*
  * The lock-class itself:
  */
@@ -114,6 +120,10 @@ struct lock_class {
 
 	const char			*name;
 	int				name_version;
+
+	atomic_t			read_contentions;
+	atomic_t			write_contentions;
+	struct lockdep_contention_point	contention_point[4];
 };
 
 /*
@@ -243,6 +253,9 @@ extern void lock_acquire(struct lockdep_
 extern void lock_release(struct lockdep_map *lock, int nested,
 			 unsigned long ip);
 
+extern void lock_contended(struct lockdep_map *lock, int read,
+			   unsigned long ip);
+
 # define INIT_LOCKDEP				.lockdep_recursion = 0,
 
 #define lockdep_depth(tsk)	(debug_locks ? (tsk)->lockdep_depth : 0)
@@ -259,6 +272,7 @@ static inline void lockdep_on(void)
 
 # define lock_acquire(l, s, t, r, c, i)		do { } while (0)
 # define lock_release(l, n, i)			do { } while (0)
+# define lock_contended(l, r, i)		do { } while (0)
 # define lockdep_init()				do { } while (0)
 # define lockdep_info()				do { } while (0)
 # define lockdep_init_map(lock, name, key, sub)	do { (void)(key); } while (0)
Index: linux-2.6/kernel/lockdep.c
===================================================================
--- linux-2.6.orig/kernel/lockdep.c	2007-05-10 17:24:41.000000000 +0200
+++ linux-2.6/kernel/lockdep.c	2007-05-19 10:58:40.000000000 +0200
@@ -2261,6 +2261,33 @@ print_unlock_inbalance_bug(struct task_s
 	return 0;
 }
 
+static int
+print_lock_contention_bug(struct task_struct *curr, struct lockdep_map *lock,
+			   unsigned long ip)
+{
+	if (!debug_locks_off())
+		return 0;
+	if (debug_locks_silent)
+		return 0;
+
+	printk("\n=================================\n");
+	printk(  "[ BUG: bad contention detected! ]\n");
+	printk(  "---------------------------------\n");
+	printk("%s/%d is trying to content lock (",
+		curr->comm, curr->pid);
+	print_lockdep_cache(lock);
+	printk(") at:\n");
+	print_ip_sym(ip);
+	printk("but there are no locks held!\n");
+	printk("\nother info that might help us debug this:\n");
+	lockdep_print_held_locks(curr);
+
+	printk("\nstack backtrace:\n");
+	dump_stack();
+
+	return 0;
+}
+
 /*
  * Common debugging checks for both nested and non-nested unlock:
  */
@@ -2401,6 +2428,59 @@ __lock_release(struct lockdep_map *lock,
 	check_chain_key(curr);
 }
 
+static void
+__lock_contended(struct lockdep_map *lock, int read, unsigned long ip)
+{
+	struct task_struct *curr = current;
+	struct held_lock *hlock, *prev_hlock;
+	struct lock_class *class;
+	unsigned int depth;
+	int i;
+
+	class = lock->class_cache;
+	if (class)
+		goto found_it;
+
+	depth = curr->lockdep_depth;
+	if (DEBUG_LOCKS_WARN_ON(!depth))
+		return;
+
+	prev_hlock = NULL;
+	for (i = depth-1; i >= 0; i--) {
+		hlock = curr->held_locks + i;
+		/*
+		 * We must not cross into another context:
+		 */
+		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
+			break;
+		if (hlock->instance == lock) {
+			class = hlock->class;
+			goto found_it;
+		}
+		prev_hlock = hlock;
+	}
+	print_lock_contention_bug(curr, lock, ip);
+	return;
+
+found_it:
+	if (read)
+		atomic_inc(&class->read_contentions);
+	else
+		atomic_inc(&class->write_contentions);
+
+	for (i = 0; i < ARRAY_SIZE(class->contention_point); i++) {
+		if (class->contention_point[i].ip == 0) {
+			class->contention_point[i].ip = ip;
+			atomic_set(&class->contention_point[i].count, 1);
+			break;
+		}
+		if (class->contention_point[i].ip == ip) {
+			atomic_inc(&class->contention_point[i].count);
+			break;
+		}
+	}
+}
+
 /*
  * Check whether we follow the irq-flags state precisely:
  */
@@ -2473,6 +2553,22 @@ void lock_release(struct lockdep_map *lo
 
 EXPORT_SYMBOL_GPL(lock_release);
 
+void lock_contended(struct lockdep_map *lock, int read, unsigned long ip)
+{
+	unsigned long flags;
+
+	if (unlikely(current->lockdep_recursion))
+		return;
+
+	raw_local_irq_save(flags);
+	check_flags(flags);
+	current->lockdep_recursion = 1;
+	__lock_contended(lock, read, ip);
+	current->lockdep_recursion = 0;
+	raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lock_contended);
+
 /*
  * Used by the testsuite, sanitize the validator state
  * after a simulated failure:
Index: linux-2.6/kernel/mutex.c
===================================================================
--- linux-2.6.orig/kernel/mutex.c	2007-05-10 10:19:03.000000000 +0200
+++ linux-2.6/kernel/mutex.c	2007-05-18 21:47:38.000000000 +0200
@@ -139,6 +139,12 @@ __mutex_lock_common(struct mutex *lock, 
 	list_add_tail(&waiter.list, &lock->wait_list);
 	waiter.task = task;
 
+	old_val = atomic_xchg(&lock->count, -1);
+	if (old_val == 1)
+		goto done;
+
+	lock_contended(&lock->dep_map, 0, _RET_IP_);
+
 	for (;;) {
 		/*
 		 * Lets try to take the lock again - this is needed even if
@@ -174,6 +180,7 @@ __mutex_lock_common(struct mutex *lock, 
 		spin_lock_mutex(&lock->wait_lock, flags);
 	}
 
+done:
 	/* got the lock - rejoice! */
 	mutex_remove_waiter(lock, &waiter, task_thread_info(task));
 	debug_mutex_set_owner(lock, task_thread_info(task));
Index: linux-2.6/kernel/lockdep_proc.c
===================================================================
--- linux-2.6.orig/kernel/lockdep_proc.c	2007-04-03 13:58:27.000000000 +0200
+++ linux-2.6/kernel/lockdep_proc.c	2007-05-19 10:50:18.000000000 +0200
@@ -15,6 +15,7 @@
 #include <linux/seq_file.h>
 #include <linux/kallsyms.h>
 #include <linux/debug_locks.h>
+#include <asm/uaccess.h>
 
 #include "lockdep_internals.h"
 
@@ -342,6 +343,78 @@ static const struct file_operations proc
 	.release	= seq_release,
 };
 
+static int lockdep_contentions_show(struct seq_file *m, void *v)
+{
+	struct lock_class *class;
+
+	list_for_each_entry(class, &all_lock_classes, lock_entry) {
+		int r, w;
+
+		r = atomic_read(&class->read_contentions);
+		w = atomic_read(&class->write_contentions);
+
+		if (r || w) {
+			int i;
+			char sym[KSYM_SYMBOL_LEN];
+
+			seq_printf(m, "%s: %d %d", class->name, w, r);
+			for (i = 0; i < ARRAY_SIZE(class->contention_point);
+					i++) {
+				struct lockdep_contention_point *cp =
+					&class->contention_point[i];
+
+				if (cp->ip == 0)
+					break;
+				sprint_symbol(sym, cp->ip);
+				seq_printf(m, " [%d] [<%p>] %s",
+						atomic_read(&cp->count),
+						(void *)cp->ip, sym);
+			}
+			seq_printf(m, "\n");
+		}
+	}
+
+	return 0;
+}
+
+static int lockdep_contentions_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, lockdep_contentions_show, NULL);
+}
+
+ssize_t lockdep_contentions_write(struct file *file, const char __user *buf,
+		size_t count, loff_t *ppos)
+{
+	struct lock_class *class;
+	char c;
+	int i;
+
+	if (count) {
+		if (get_user(c, buf))
+			return -EFAULT;
+
+		if (c != '0')
+			return count;
+
+		list_for_each_entry(class, &all_lock_classes, lock_entry) {
+			atomic_set(&class->write_contentions, 0);
+			atomic_set(&class->read_contentions, 0);
+			for (i = 0; i < ARRAY_SIZE(class->contention_point);
+					i++)
+				class->contention_point[i].ip = 0;
+		}
+	}
+	return count;
+}
+
+static const struct file_operations proc_lockdep_contentions_operations = {
+	.open		= lockdep_contentions_open,
+	.write		= lockdep_contentions_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
 static int __init lockdep_proc_init(void)
 {
 	struct proc_dir_entry *entry;
@@ -354,6 +427,10 @@ static int __init lockdep_proc_init(void
 	if (entry)
 		entry->proc_fops = &proc_lockdep_stats_operations;
 
+	entry = create_proc_entry("lockdep_contentions", S_IRUSR, NULL);
+	if (entry)
+		entry->proc_fops = &proc_lockdep_contentions_operations;
+
 	return 0;
 }
 
Index: linux-2.6/kernel/rwsem.c
===================================================================
--- linux-2.6.orig/kernel/rwsem.c	2007-05-19 10:06:44.000000000 +0200
+++ linux-2.6/kernel/rwsem.c	2007-05-19 10:37:59.000000000 +0200
@@ -20,7 +20,10 @@ void down_read(struct rw_semaphore *sem)
 	might_sleep();
 	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
 
-	__down_read(sem);
+	if (!__down_read_trylock(sem)) {
+		lock_contended(&sem->dep_map, 1, _RET_IP_);
+		__down_read(sem);
+	}
 }
 
 EXPORT_SYMBOL(down_read);
@@ -47,7 +50,10 @@ void down_write(struct rw_semaphore *sem
 	might_sleep();
 	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
 
-	__down_write(sem);
+	if (!__down_write_trylock(sem)) {
+		lock_contended(&sem->dep_map, 0, _RET_IP_);
+		__down_write(sem);
+	}
 }
 
 EXPORT_SYMBOL(down_write);
@@ -111,7 +117,10 @@ void down_read_nested(struct rw_semaphor
 	might_sleep();
 	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 
-	__down_read(sem);
+	if (!__down_read_trylock(sem)) {
+		lock_contended(&sem->dep_map, 1, _RET_IP_);
+		__down_read(sem);
+	}
 }
 
 EXPORT_SYMBOL(down_read_nested);
@@ -130,7 +139,10 @@ void down_write_nested(struct rw_semapho
 	might_sleep();
 	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 
-	__down_write_nested(sem, subclass);
+	if (!__down_write_trylock(sem)) {
+		lock_contended(&sem->dep_map, 0, _RET_IP_);
+		__down_write_nested(sem, subclass);
+	}
 }
 
 EXPORT_SYMBOL(down_write_nested);
Index: linux-2.6/kernel/spinlock.c
===================================================================
--- linux-2.6.orig/kernel/spinlock.c	2007-05-10 10:19:03.000000000 +0200
+++ linux-2.6/kernel/spinlock.c	2007-05-19 10:20:47.000000000 +0200
@@ -72,7 +72,10 @@ void __lockfunc _read_lock(rwlock_t *loc
 {
 	preempt_disable();
 	rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_read_lock(lock);
+	if (!_raw_read_trylock(lock)) {
+		lock_contended(&lock->dep_map, 1, _RET_IP_);
+		_raw_read_lock(lock);
+	}
 }
 EXPORT_SYMBOL(_read_lock);
 
@@ -89,7 +92,10 @@ unsigned long __lockfunc _spin_lock_irqs
 	 * that interrupts are not re-enabled during lock-acquire:
 	 */
 #ifdef CONFIG_PROVE_LOCKING
-	_raw_spin_lock(lock);
+	if (!_raw_spin_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_spin_lock(lock);
+	}
 #else
 	_raw_spin_lock_flags(lock, &flags);
 #endif
@@ -102,7 +108,10 @@ void __lockfunc _spin_lock_irq(spinlock_
 	local_irq_disable();
 	preempt_disable();
 	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_spin_lock(lock);
+	if (!_raw_spin_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_spin_lock(lock);
+	}
 }
 EXPORT_SYMBOL(_spin_lock_irq);
 
@@ -111,7 +120,10 @@ void __lockfunc _spin_lock_bh(spinlock_t
 	local_bh_disable();
 	preempt_disable();
 	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_spin_lock(lock);
+	if (!_raw_spin_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_spin_lock(lock);
+	}
 }
 EXPORT_SYMBOL(_spin_lock_bh);
 
@@ -122,7 +134,10 @@ unsigned long __lockfunc _read_lock_irqs
 	local_irq_save(flags);
 	preempt_disable();
 	rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_read_lock(lock);
+	if (!_raw_read_trylock(lock)) {
+		lock_contended(&lock->dep_map, 1, _RET_IP_);
+		_raw_read_lock(lock);
+	}
 	return flags;
 }
 EXPORT_SYMBOL(_read_lock_irqsave);
@@ -132,7 +147,10 @@ void __lockfunc _read_lock_irq(rwlock_t 
 	local_irq_disable();
 	preempt_disable();
 	rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_read_lock(lock);
+	if (!_raw_read_trylock(lock)) {
+		lock_contended(&lock->dep_map, 1, _RET_IP_);
+		_raw_read_lock(lock);
+	}
 }
 EXPORT_SYMBOL(_read_lock_irq);
 
@@ -141,7 +159,10 @@ void __lockfunc _read_lock_bh(rwlock_t *
 	local_bh_disable();
 	preempt_disable();
 	rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_read_lock(lock);
+	if (!_raw_read_trylock(lock)) {
+		lock_contended(&lock->dep_map, 1, _RET_IP_);
+		_raw_read_lock(lock);
+	}
 }
 EXPORT_SYMBOL(_read_lock_bh);
 
@@ -152,7 +173,10 @@ unsigned long __lockfunc _write_lock_irq
 	local_irq_save(flags);
 	preempt_disable();
 	rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_write_lock(lock);
+	if (!_raw_write_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_write_lock(lock);
+	}
 	return flags;
 }
 EXPORT_SYMBOL(_write_lock_irqsave);
@@ -162,7 +186,10 @@ void __lockfunc _write_lock_irq(rwlock_t
 	local_irq_disable();
 	preempt_disable();
 	rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_write_lock(lock);
+	if (!_raw_write_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_write_lock(lock);
+	}
 }
 EXPORT_SYMBOL(_write_lock_irq);
 
@@ -171,7 +198,10 @@ void __lockfunc _write_lock_bh(rwlock_t 
 	local_bh_disable();
 	preempt_disable();
 	rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_write_lock(lock);
+	if (!_raw_write_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_write_lock(lock);
+	}
 }
 EXPORT_SYMBOL(_write_lock_bh);
 
@@ -179,7 +209,10 @@ void __lockfunc _spin_lock(spinlock_t *l
 {
 	preempt_disable();
 	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_spin_lock(lock);
+	if (!_raw_spin_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_spin_lock(lock);
+	}
 }
 
 EXPORT_SYMBOL(_spin_lock);
@@ -188,7 +221,10 @@ void __lockfunc _write_lock(rwlock_t *lo
 {
 	preempt_disable();
 	rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
-	_raw_write_lock(lock);
+	if (!_raw_write_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_write_lock(lock);
+	}
 }
 
 EXPORT_SYMBOL(_write_lock);
@@ -289,7 +325,10 @@ void __lockfunc _spin_lock_nested(spinlo
 {
 	preempt_disable();
 	spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
-	_raw_spin_lock(lock);
+	if (!_raw_spin_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_spin_lock(lock);
+	}
 }
 
 EXPORT_SYMBOL(_spin_lock_nested);
@@ -306,7 +345,10 @@ unsigned long __lockfunc _spin_lock_irqs
 	 * that interrupts are not re-enabled during lock-acquire:
 	 */
 #ifdef CONFIG_PROVE_SPIN_LOCKING
-	_raw_spin_lock(lock);
+	if (!_raw_spin_trylock(lock)) {
+		lock_contended(&lock->dep_map, 0, _RET_IP_);
+		_raw_spin_lock(lock);
+	}
 #else
 	_raw_spin_lock_flags(lock, &flags);
 #endif


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