Date:	Fri, 20 Jun 2008 16:39:21 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] lockdep: add lock_class information to lock_chain and
	output it

This patch is not intended to be merged. Just hope it is useful for
somebody want to investigate kernel locking behavior. The simple
scripts attached with the mail can be used to draw class chain graph
via graphviz.

Best Regards,
Huang Ying
------------------------------------------------------------->
This patch records array of lock_class into lock_chain, and export
lock_chain information via /proc/lockdep_chains.

It is based on x86/master branch of git-x86 tree, and has been tested
on x86_64 platform.

Signed-off-by: Huang Ying <ying.huang@...el.com>

---
 include/linux/lockdep.h    |    3 +
 kernel/lockdep.c           |   38 +++++++++++++++++-
 kernel/lockdep_internals.h |    6 ++
 kernel/lockdep_proc.c      |   91 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 135 insertions(+), 3 deletions(-)

--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -1463,7 +1463,14 @@ out_bug:
 }
 
 unsigned long nr_lock_chains;
-static struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
+struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
+atomic_t nr_chain_hlocks;
+static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
+
+struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
+{
+	return lock_classes + chain_hlocks[chain->base + i];
+}
 
 /*
  * Look up a dependency chain. If the key is not present yet then
@@ -1471,10 +1478,15 @@ static struct lock_chain lock_chains[MAX
  * validated. If the key is already hashed, return 0.
  * (On return with 1 graph_lock is held.)
  */
-static inline int lookup_chain_cache(u64 chain_key, struct lock_class *class)
+static inline int lookup_chain_cache(struct task_struct *curr,
+				     struct held_lock *hlock,
+				     u64 chain_key)
 {
+	struct lock_class *class = hlock->class;
 	struct list_head *hash_head = chainhashentry(chain_key);
 	struct lock_chain *chain;
+	struct held_lock *hlock_curr, *hlock_next;
+	int i, j, n;
 
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
 		return 0;
@@ -1522,6 +1534,26 @@ cache_hit:
 	}
 	chain = lock_chains + nr_lock_chains++;
 	chain->chain_key = chain_key;
+	chain->irq_context = hlock->irq_context;
+	/* Find the first held_lock of current chain */
+	hlock_next = hlock;
+	for (i = curr->lockdep_depth - 1; i >= 0; i--) {
+		hlock_curr = curr->held_locks + i;
+		if (hlock_curr->irq_context != hlock_next->irq_context)
+			break;
+		hlock_next = hlock;
+	}
+	i++;
+	chain->depth = curr->lockdep_depth + 1 - i;
+	n = atomic_add_return(chain->depth, &nr_chain_hlocks);
+	if (unlikely(n < MAX_LOCKDEP_CHAIN_HLOCKS)) {
+		chain->base = n - chain->depth;
+		for (j = 0; j < chain->depth - 1; j++, i++) {
+			int lock_id = curr->held_locks[i].class - lock_classes;
+			chain_hlocks[chain->base + j] = lock_id;
+		}
+		chain_hlocks[chain->base + j] = class - lock_classes;
+	}
 	list_add_tail_rcu(&chain->entry, hash_head);
 	debug_atomic_inc(&chain_lookup_misses);
 	inc_chains();
@@ -1543,7 +1575,7 @@ static int validate_chain(struct task_st
 	 * graph_lock for us)
 	 */
 	if (!hlock->trylock && (hlock->check == 2) &&
-			lookup_chain_cache(chain_key, hlock->class)) {
+	    lookup_chain_cache(curr, hlock, chain_key)) {
 		/*
 		 * Check whether last held lock:
 		 *
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -182,6 +182,9 @@ struct lock_list {
  * We record lock dependency chains, so that we can cache them:
  */
 struct lock_chain {
+	u8				irq_context;
+	u8				depth;
+	u16				base;
 	struct list_head		entry;
 	u64				chain_key;
 };
--- a/kernel/lockdep_proc.c
+++ b/kernel/lockdep_proc.c
@@ -178,6 +178,93 @@ static const struct file_operations proc
 	.release	= seq_release,
 };
 
+static void *lc_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct lock_chain *chain;
+
+	(*pos)++;
+
+	if (v == SEQ_START_TOKEN)
+		chain = m->private;
+	else {
+		chain = v;
+
+		if (*pos < nr_lock_chains)
+			chain = lock_chains + *pos;
+		else
+			chain = NULL;
+	}
+
+	return chain;
+}
+
+static void *lc_start(struct seq_file *m, loff_t *pos)
+{
+	if (*pos == 0)
+		return SEQ_START_TOKEN;
+
+	if (*pos < nr_lock_chains)
+		return lock_chains + *pos;
+
+	return NULL;
+}
+
+static void lc_stop(struct seq_file *m, void *v)
+{
+}
+
+static int lc_show(struct seq_file *m, void *v)
+{
+	struct lock_chain *chain = v;
+	struct lock_class *class;
+	int i;
+
+	if (v == SEQ_START_TOKEN) {
+		seq_printf(m, "all lock chains:\n");
+		return 0;
+	}
+
+	seq_printf(m, "irq_context: %d\n", chain->irq_context);
+
+	for (i = 0; i < chain->depth; i++) {
+		class = lock_chain_get_class(chain, i);
+		seq_printf(m, "[%p] ", class->key);
+		print_name(m, class);
+		seq_puts(m, "\n");
+	}
+	seq_puts(m, "\n");
+
+	return 0;
+}
+
+static const struct seq_operations lockdep_chains_ops = {
+	.start	= lc_start,
+	.next	= lc_next,
+	.stop	= lc_stop,
+	.show	= lc_show,
+};
+
+static int lockdep_chains_open(struct inode *inode, struct file *file)
+{
+	int res = seq_open(file, &lockdep_chains_ops);
+	if (!res) {
+		struct seq_file *m = file->private_data;
+
+		if (nr_lock_chains)
+			m->private = lock_chains;
+		else
+			m->private = NULL;
+	}
+	return res;
+}
+
+static const struct file_operations proc_lockdep_chains_operations = {
+	.open		= lockdep_chains_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
 static void lockdep_stats_debug_show(struct seq_file *m)
 {
 #ifdef CONFIG_DEBUG_LOCKDEP
@@ -294,6 +381,8 @@ static int lockdep_stats_show(struct seq
 #ifdef CONFIG_PROVE_LOCKING
 	seq_printf(m, " dependency chains:             %11lu [max: %lu]\n",
 			nr_lock_chains, MAX_LOCKDEP_CHAINS);
+	seq_printf(m, " dependency chain hlocks:       %11d [max: %lu]\n",
+			atomic_read(&nr_chain_hlocks), MAX_LOCKDEP_CHAIN_HLOCKS);
 #endif
 
 #ifdef CONFIG_TRACE_IRQFLAGS
@@ -661,6 +750,8 @@ static const struct file_operations proc
 static int __init lockdep_proc_init(void)
 {
 	proc_create("lockdep", S_IRUSR, NULL, &proc_lockdep_operations);
+	proc_create("lockdep_chains", S_IRUSR, NULL,
+		    &proc_lockdep_chains_operations);
 	proc_create("lockdep_stats", S_IRUSR, NULL,
 		    &proc_lockdep_stats_operations);
 
--- a/kernel/lockdep_internals.h
+++ b/kernel/lockdep_internals.h
@@ -23,6 +23,8 @@
 #define MAX_LOCKDEP_CHAINS_BITS	14
 #define MAX_LOCKDEP_CHAINS	(1UL << MAX_LOCKDEP_CHAINS_BITS)
 
+#define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5)
+
 /*
  * Stack-trace: tightly packed array of stack backtrace
  * addresses. Protected by the hash_lock.
@@ -30,15 +32,19 @@
 #define MAX_STACK_TRACE_ENTRIES	262144UL
 
 extern struct list_head all_lock_classes;
+extern struct lock_chain lock_chains[];
 
 extern void
 get_usage_chars(struct lock_class *class, char *c1, char *c2, char *c3, char *c4);
 
 extern const char * __get_key_name(struct lockdep_subclass_key *key, char *str);
 
+struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i);
+
 extern unsigned long nr_lock_classes;
 extern unsigned long nr_list_entries;
 extern unsigned long nr_lock_chains;
+extern atomic_t nr_chain_hlocks;
 extern unsigned long nr_stack_trace_entries;
 
 extern unsigned int nr_hardirq_chains;


View attachment "lockdep.py" of type "text/x-python" (6946 bytes)

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