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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>
wifi-calibration
David Miller 2008-07-29 21:45:03 -07:00 committed by Ingo Molnar
parent 6e86841d05
commit 419ca3f135
4 changed files with 93 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/lockdep.h
View File

@ -89,6 +89,7 @@ struct lock_class {
struct lockdep_subclass_key *key;
unsigned int subclass;
unsigned int dep_gen_id;
/*
* IRQ/softirq usage tracking bits:

86
kernel/lockdep.c
View File

@ -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);

3
kernel/lockdep_internals.h
View File

@ -53,6 +53,9 @@ extern unsigned int nr_process_chains;
extern unsigned int max_lockdep_depth;
extern unsigned int max_recursion_depth;
extern unsigned long lockdep_count_forward_deps(struct lock_class *);
extern unsigned long lockdep_count_backward_deps(struct lock_class *);
#ifdef CONFIG_DEBUG_LOCKDEP
/*
* Various lockdep statistics:

34
kernel/lockdep_proc.c
View File

@ -63,34 +63,6 @@ static void l_stop(struct seq_file *m, void *v)
{
}
static unsigned long count_forward_deps(struct lock_class *class)
{
struct lock_list *entry;
unsigned long ret = 1;
/*
* Recurse this class's dependency list:
*/
list_for_each_entry(entry, &class->locks_after, entry)
ret += count_forward_deps(entry->class);
return ret;
}
static unsigned long count_backward_deps(struct lock_class *class)
{
struct lock_list *entry;
unsigned long ret = 1;
/*
* Recurse this class's dependency list:
*/
list_for_each_entry(entry, &class->locks_before, entry)
ret += count_backward_deps(entry->class);
return ret;
}
static void print_name(struct seq_file *m, struct lock_class *class)
{
char str[128];
@ -124,10 +96,10 @@ static int l_show(struct seq_file *m, void *v)
#ifdef CONFIG_DEBUG_LOCKDEP
seq_printf(m, " OPS:%8ld", class->ops);
#endif
nr_forward_deps = count_forward_deps(class);
nr_forward_deps = lockdep_count_forward_deps(class);
seq_printf(m, " FD:%5ld", nr_forward_deps);
nr_backward_deps = count_backward_deps(class);
nr_backward_deps = lockdep_count_backward_deps(class);
seq_printf(m, " BD:%5ld", nr_backward_deps);
get_usage_chars(class, &c1, &c2, &c3, &c4);
@ -350,7 +322,7 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
if (class->usage_mask & LOCKF_ENABLED_HARDIRQS_READ)
nr_hardirq_read_unsafe++;
sum_forward_deps += count_forward_deps(class);
sum_forward_deps += lockdep_count_forward_deps(class);
}
#ifdef CONFIG_DEBUG_LOCKDEP
DEBUG_LOCKS_WARN_ON(debug_atomic_read(&nr_unused_locks) != nr_unused);