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Subject[tip:core/locking] lockdep: Implement check_noncircular() by BFS
Commit-ID:  db0002a32f31060ca900b533d93a074ddf7d5b61
Gitweb: http://git.kernel.org/tip/db0002a32f31060ca900b533d93a074ddf7d5b61
Author: Ming Lei <tom.leiming@gmail.com>
AuthorDate: Thu, 16 Jul 2009 15:44:29 +0200
Committer: Peter Zijlstra <a.p.zijlstra@chello.nl>
CommitDate: Fri, 24 Jul 2009 10:49:50 +0200

lockdep: Implement check_noncircular() by BFS

This patch uses BFS to implement check_noncircular() and
prints the generated shortest circle if exists.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1246201486-7308-5-git-send-email-tom.leiming@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
kernel/lockdep.c | 89 ++++++++++++++++++++++-------------------------------
1 files changed, 37 insertions(+), 52 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index ce6d09e..5609d30 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -985,12 +985,7 @@ static inline int __bfs_backward(struct lock_list *src_entry,
* 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
@@ -1014,7 +1009,9 @@ print_circular_bug_entry(struct lock_list *target, unsigned int depth)
* header first:
*/
static noinline int
-print_circular_bug_header(struct lock_list *entry, unsigned int depth)
+print_circular_bug_header(struct lock_list *entry, unsigned int depth,
+ struct held_lock *check_src,
+ struct held_lock *check_tgt)
{
struct task_struct *curr = current;

@@ -1027,9 +1024,9 @@ print_circular_bug_header(struct lock_list *entry, unsigned int depth)
printk( "-------------------------------------------------------\n");
printk("%s/%d is trying to acquire lock:\n",
curr->comm, task_pid_nr(curr));
- print_lock(check_source);
+ print_lock(check_src);
printk("\nbut task is already holding lock:\n");
- print_lock(check_target);
+ print_lock(check_tgt);
printk("\nwhich lock already depends on the new lock.\n\n");
printk("\nthe existing dependency chain (in reverse order) is:\n");

@@ -1043,36 +1040,24 @@ static inline int class_equal(struct lock_list *entry, void *data)
return entry->class == data;
}

-static noinline int print_circular_bug(void)
+static noinline int print_circular_bug(struct lock_list *this,
+ struct lock_list *target,
+ struct held_lock *check_src,
+ struct held_lock *check_tgt)
{
struct task_struct *curr = current;
- struct lock_list this;
- struct lock_list *target;
struct lock_list *parent;
- int result;
unsigned long depth;

if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return 0;

- this.class = hlock_class(check_source);
- this.parent = NULL;
- if (!save_trace(&this.trace))
+ if (!save_trace(&this->trace))
return 0;

- result = __bfs_forward(&this,
- hlock_class(check_target),
- class_equal,
- &target);
- if (result) {
- printk("\n%s:search shortest path failed:%d\n", __func__,
- result);
- return 0;
- }
-
depth = get_lock_depth(target);

- print_circular_bug_header(target, depth);
+ print_circular_bug_header(target, depth, check_src, check_tgt);

parent = get_lock_parent(target);

@@ -1090,6 +1075,16 @@ static noinline int print_circular_bug(void)
return 0;
}

+static noinline int print_bfs_bug(int ret)
+{
+ if (!debug_locks_off_graph_unlock())
+ return 0;
+
+ WARN(1, "lockdep bfs error:%d\n", ret);
+
+ return 0;
+}
+
#define RECURSION_LIMIT 40

static int noinline print_infinite_recursion_bug(void)
@@ -1168,31 +1163,17 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
* lead to <target>. Print an error and return 0 if it does.
*/
static noinline int
-check_noncircular(struct lock_class *source, unsigned int depth)
+check_noncircular(struct lock_list *root, struct lock_class *target,
+ struct lock_list **target_entry)
{
- struct lock_list *entry;
+ int result;

- if (lockdep_dependency_visit(source, depth))
- return 1;
+ debug_atomic_inc(&nr_cyclic_checks);

- debug_atomic_inc(&nr_cyclic_check_recursions);
- if (depth > max_recursion_depth)
- max_recursion_depth = depth;
- if (depth >= RECURSION_LIMIT)
- return print_infinite_recursion_bug();
- /*
- * Check this lock's dependency list:
- */
- list_for_each_entry(entry, &source->locks_after, entry) {
- if (entry->class == hlock_class(check_target))
- return 2;
- debug_atomic_inc(&nr_cyclic_checks);
- if (check_noncircular(entry->class, depth+1) == 2)
- return 2;
- }
- return 1;
-}
+ result = __bfs_forward(root, target, class_equal, target_entry);

+ return result;
+}

#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
/*
@@ -1586,6 +1567,8 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
{
struct lock_list *entry;
int ret;
+ struct lock_list this;
+ struct lock_list *uninitialized_var(target_entry);

/*
* Prove that the new <prev> -> <next> dependency would not
@@ -1596,11 +1579,13 @@ check_prev_add(struct task_struct *curr, struct held_lock *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(hlock_class(next), 0) == 2)
- return print_circular_bug();
+ this.class = hlock_class(next);
+ this.parent = NULL;
+ ret = check_noncircular(&this, hlock_class(prev), &target_entry);
+ if (unlikely(!ret))
+ return print_circular_bug(&this, target_entry, next, prev);
+ else if (unlikely(ret < 0))
+ return print_bfs_bug(ret);

if (!check_prev_add_irq(curr, prev, next))
return 0;

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