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authorDavid Miller <davem@davemloft.net>2008-07-29 21:45:03 -0700
committerIngo Molnar <mingo@elte.hu>2008-07-31 18:38:28 +0200
commit419ca3f13532793b81aff09f80c60af3eacbb43d (patch)
treeeb2d82e52917ebccff269a51e90868ce229336b2 /kernel/lockdep.c
parent6e86841d05f371b5b9b86ce76c02aaee83352298 (diff)
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lockdep: fix combinatorial explosion in lock subgraph traversal
When we traverse the graph, either forwards or backwards, we are interested in whether a certain property exists somewhere in a node reachable in the graph. Therefore it is never necessary to traverse through a node more than once to get a correct answer to the given query. Take advantage of this property using a global ID counter so that we need not clear all the markers in all the lock_class entries before doing a traversal. A new ID is choosen when we start to traverse, and we continue through a lock_class only if it's ID hasn't been marked with the new value yet. This short-circuiting is essential especially for high CPU count systems. The scheduler has a runqueue per cpu, and needs to take two runqueue locks at a time, which leads to long chains of backwards and forwards subgraphs from these runqueue lock nodes. Without the short-circuit implemented here, a graph traversal on a runqueue lock can take up to (1 << (N - 1)) checks on a system with N cpus. For anything more than 16 cpus or so, lockdep will eventually bring the machine to a complete standstill. Signed-off-by: David S. Miller <davem@davemloft.net> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/lockdep.c')
-rw-r--r--kernel/lockdep.c86
1 files changed, 86 insertions, 0 deletions
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index d38a643..6999e64 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -372,6 +372,19 @@ unsigned int nr_process_chains;
unsigned int max_lockdep_depth;
unsigned int max_recursion_depth;
+static unsigned int lockdep_dependency_gen_id;
+
+static bool lockdep_dependency_visit(struct lock_class *source,
+ unsigned int depth)
+{
+ if (!depth)
+ lockdep_dependency_gen_id++;
+ if (source->dep_gen_id == lockdep_dependency_gen_id)
+ return true;
+ source->dep_gen_id = lockdep_dependency_gen_id;
+ return false;
+}
+
#ifdef CONFIG_DEBUG_LOCKDEP
/*
* We cannot printk in early bootup code. Not even early_printk()
@@ -558,6 +571,9 @@ static void print_lock_dependencies(struct lock_class *class, int depth)
{
struct lock_list *entry;
+ if (lockdep_dependency_visit(class, depth))
+ return;
+
if (DEBUG_LOCKS_WARN_ON(depth >= 20))
return;
@@ -959,6 +975,67 @@ static int noinline print_infinite_recursion_bug(void)
return 0;
}
+unsigned long __lockdep_count_forward_deps(struct lock_class *class,
+ unsigned int depth)
+{
+ struct lock_list *entry;
+ unsigned long ret = 1;
+
+ if (lockdep_dependency_visit(class, depth))
+ return 0;
+
+ /*
+ * Recurse this class's dependency list:
+ */
+ list_for_each_entry(entry, &class->locks_after, entry)
+ ret += __lockdep_count_forward_deps(entry->class, depth + 1);
+
+ return ret;
+}
+
+unsigned long lockdep_count_forward_deps(struct lock_class *class)
+{
+ unsigned long ret, flags;
+
+ local_irq_save(flags);
+ __raw_spin_lock(&lockdep_lock);
+ ret = __lockdep_count_forward_deps(class, 0);
+ __raw_spin_unlock(&lockdep_lock);
+ local_irq_restore(flags);
+
+ return ret;
+}
+
+unsigned long __lockdep_count_backward_deps(struct lock_class *class,
+ unsigned int depth)
+{
+ struct lock_list *entry;
+ unsigned long ret = 1;
+
+ if (lockdep_dependency_visit(class, depth))
+ return 0;
+ /*
+ * Recurse this class's dependency list:
+ */
+ list_for_each_entry(entry, &class->locks_before, entry)
+ ret += __lockdep_count_backward_deps(entry->class, depth + 1);
+
+ return ret;
+}
+
+unsigned long lockdep_count_backward_deps(struct lock_class *class)
+{
+ unsigned long ret, flags;
+
+ local_irq_save(flags);
+ __raw_spin_lock(&lockdep_lock);
+ ret = __lockdep_count_backward_deps(class, 0);
+ __raw_spin_unlock(&lockdep_lock);
+ local_irq_restore(flags);
+
+ return ret;
+}
+
/*
* Prove that the dependency graph starting at <entry> can not
* lead to <target>. Print an error and return 0 if it does.
@@ -968,6 +1045,9 @@ check_noncircular(struct lock_class *source, unsigned int depth)
{
struct lock_list *entry;
+ if (lockdep_dependency_visit(source, depth))
+ return 1;
+
debug_atomic_inc(&nr_cyclic_check_recursions);
if (depth > max_recursion_depth)
max_recursion_depth = depth;
@@ -1011,6 +1091,9 @@ find_usage_forwards(struct lock_class *source, unsigned int depth)
struct lock_list *entry;
int ret;
+ if (lockdep_dependency_visit(source, depth))
+ return 1;
+
if (depth > max_recursion_depth)
max_recursion_depth = depth;
if (depth >= RECURSION_LIMIT)
@@ -1050,6 +1133,9 @@ find_usage_backwards(struct lock_class *source, unsigned int depth)
struct lock_list *entry;
int ret;
+ if (lockdep_dependency_visit(source, depth))
+ return 1;
+
if (!__raw_spin_is_locked(&lockdep_lock))
return DEBUG_LOCKS_WARN_ON(1);