[RFC tip/locking/lockdep v3 01/14] lockdep: Demagic the return value of BFS

From: Boqun Feng
Date: Mon Sep 25 2017 - 18:18:23 EST

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__bfs() could return four magic numbers:

1: search succeeds, but none match.
0: search succeeds, find one match.
-1: search fails because of the cq is full.
-2: search fails because a invalid node is found.

This patch cleans things up by using a enum type for the return value
of __bfs() and its friends, this improves the code readability of the
code, and further, could help if we want to extend the BFS.

Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
---
kernel/locking/lockdep.c | 134 ++++++++++++++++++++++++++++-------------------
1 file changed, 79 insertions(+), 55 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 44c8d0d17170..df0b7e620659 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -996,21 +996,52 @@ static inline int get_lock_depth(struct lock_list *child)
}
return depth;
}
+/*
+ * Return values of a bfs search:
+ *
+ * BFS_E* indicates an error
+ * BFS_R* indicates a result(match or not)
+ *
+ * BFS_EINVALIDNODE: Find a invalid node in the graph.
+ *
+ * BFS_EQUEUEFULL: The queue is full while doing the bfs.
+ *
+ * BFS_RMATCH: Find the matched node in the graph, and put that node * into
+ * *@target_entry.
+ *
+ * BFS_RNOMATCH: Haven't found the matched node and keep *@target_entry
+ * _unchanged_.
+ */
+enum bfs_result {
+ BFS_EINVALIDNODE = -2,
+ BFS_EQUEUEFULL = -1,
+ BFS_RMATCH = 0,
+ BFS_RNOMATCH = 1,
+};
+
+/*
+ * bfs_result < 0 means error
+ */
+
+static inline bool bfs_error(enum bfs_result res)
+{
+ return res < 0;
+}

-static int __bfs(struct lock_list *source_entry,
- void *data,
- int (*match)(struct lock_list *entry, void *data),
- struct lock_list **target_entry,
- int forward)
+static enum bfs_result __bfs(struct lock_list *source_entry,
+ void *data,
+ int (*match)(struct lock_list *entry, void *data),
+ struct lock_list **target_entry,
+ int forward)
{
struct lock_list *entry;
struct list_head *head;
struct circular_queue *cq = &lock_cq;
- int ret = 1;
+ enum bfs_result ret = BFS_RNOMATCH;

if (match(source_entry, data)) {
*target_entry = source_entry;
- ret = 0;
+ ret = BFS_RMATCH;
goto exit;
}

@@ -1031,7 +1062,7 @@ static int __bfs(struct lock_list *source_entry,
__cq_dequeue(cq, (unsigned long *)&lock);

if (!lock->class) {
- ret = -2;
+ ret = BFS_EINVALIDNODE;
goto exit;
}

@@ -1048,12 +1079,12 @@ static int __bfs(struct lock_list *source_entry,
mark_lock_accessed(entry, lock);
if (match(entry, data)) {
*target_entry = entry;
- ret = 0;
+ ret = BFS_RMATCH;
goto exit;
}

if (__cq_enqueue(cq, (unsigned long)entry)) {
- ret = -1;
+ ret = BFS_EQUEUEFULL;
goto exit;
}
cq_depth = __cq_get_elem_count(cq);
@@ -1066,19 +1097,21 @@ static int __bfs(struct lock_list *source_entry,
return ret;
}

-static inline int __bfs_forwards(struct lock_list *src_entry,
- void *data,
- int (*match)(struct lock_list *entry, void *data),
- struct lock_list **target_entry)
+static inline enum bfs_result
+__bfs_forwards(struct lock_list *src_entry,
+ void *data,
+ int (*match)(struct lock_list *entry, void *data),
+ struct lock_list **target_entry)
{
return __bfs(src_entry, data, match, target_entry, 1);

}

-static inline int __bfs_backwards(struct lock_list *src_entry,
- void *data,
- int (*match)(struct lock_list *entry, void *data),
- struct lock_list **target_entry)
+static inline enum bfs_result
+__bfs_backwards(struct lock_list *src_entry,
+ void *data,
+ int (*match)(struct lock_list *entry, void *data),
+ struct lock_list **target_entry)
{
return __bfs(src_entry, data, match, target_entry, 0);

@@ -1335,13 +1368,13 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)

/*
* Prove that the dependency graph starting at <entry> can not
- * lead to <target>. Print an error and return 0 if it does.
+ * lead to <target>. Print an error and return BFS_RMATCH if it does.
*/
-static noinline int
+static noinline enum bfs_result
check_noncircular(struct lock_list *root, struct lock_class *target,
- struct lock_list **target_entry)
+ struct lock_list **target_entry)
{
- int result;
+ enum bfs_result result;

debug_atomic_inc(nr_cyclic_checks);

@@ -1350,11 +1383,11 @@ check_noncircular(struct lock_list *root, struct lock_class *target,
return result;
}

-static noinline int
+static noinline enum bfs_result
check_redundant(struct lock_list *root, struct lock_class *target,
struct lock_list **target_entry)
{
- int result;
+ enum bfs_result result;

debug_atomic_inc(nr_redundant_checks);

@@ -1383,15 +1416,12 @@ static inline int usage_match(struct lock_list *entry, void *bit)
*
* Return 0 if such a node exists in the subgraph, and put that node
* into *@target_entry.
- *
- * Return 1 otherwise and keep *@target_entry unchanged.
- * Return <0 on error.
*/
-static int
+static enum bfs_result
find_usage_forwards(struct lock_list *root, enum lock_usage_bit bit,
struct lock_list **target_entry)
{
- int result;
+ enum bfs_result result;

debug_atomic_inc(nr_find_usage_forwards_checks);

@@ -1403,18 +1433,12 @@ find_usage_forwards(struct lock_list *root, enum lock_usage_bit bit,
/*
* Find a node in the backwards-direction dependency sub-graph starting
* at @root->class that matches @bit.
- *
- * Return 0 if such a node exists in the subgraph, and put that node
- * into *@target_entry.
- *
- * Return 1 otherwise and keep *@target_entry unchanged.
- * Return <0 on error.
*/
-static int
+static enum bfs_result
find_usage_backwards(struct lock_list *root, enum lock_usage_bit bit,
struct lock_list **target_entry)
{
- int result;
+ enum bfs_result result;

debug_atomic_inc(nr_find_usage_backwards_checks);

@@ -1622,18 +1646,18 @@ check_usage(struct task_struct *curr, struct held_lock *prev,

this.class = hlock_class(prev);
ret = find_usage_backwards(&this, bit_backwards, &target_entry);
- if (ret < 0)
+ if (bfs_error(ret))
return print_bfs_bug(ret);
- if (ret == 1)
- return ret;
+ if (ret == BFS_RNOMATCH)
+ return 1;

that.parent = NULL;
that.class = hlock_class(next);
ret = find_usage_forwards(&that, bit_forwards, &target_entry1);
- if (ret < 0)
+ if (bfs_error(ret))
return print_bfs_bug(ret);
- if (ret == 1)
- return ret;
+ if (ret == BFS_RNOMATCH)
+ return 1;

return print_bad_irq_dependency(curr, &this, &that,
target_entry, target_entry1,
@@ -1874,7 +1898,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
int (*save)(struct stack_trace *trace))
{
struct lock_list *entry;
- int ret;
+ enum bfs_result ret;
struct lock_list this;
struct lock_list *uninitialized_var(target_entry);

@@ -1890,9 +1914,9 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
this.class = hlock_class(next);
this.parent = NULL;
ret = check_noncircular(&this, hlock_class(prev), &target_entry);
- if (unlikely(!ret))
+ if (unlikely(ret == BFS_RMATCH))
return print_circular_bug(&this, target_entry, next, prev, trace);
- else if (unlikely(ret < 0))
+ else if (unlikely(bfs_error(ret)))
return print_bfs_bug(ret);

if (!check_prev_add_irq(curr, prev, next))
@@ -1930,11 +1954,11 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
this.class = hlock_class(prev);
this.parent = NULL;
ret = check_redundant(&this, hlock_class(next), &target_entry);
- if (!ret) {
+ if (ret == BFS_RMATCH) {
debug_atomic_inc(nr_redundant);
return 2;
}
- if (ret < 0)
+ if (bfs_error(ret))
return print_bfs_bug(ret);

@@ -2685,16 +2709,16 @@ static int
check_usage_forwards(struct task_struct *curr, struct held_lock *this,
enum lock_usage_bit bit, const char *irqclass)
{
- int ret;
+ enum bfs_result ret;
struct lock_list root;
struct lock_list *uninitialized_var(target_entry);

root.parent = NULL;
root.class = hlock_class(this);
ret = find_usage_forwards(&root, bit, &target_entry);
- if (ret < 0)
+ if (bfs_error(ret))
return print_bfs_bug(ret);
- if (ret == 1)
+ if (ret == BFS_RNOMATCH)
return ret;

return print_irq_inversion_bug(curr, &root, target_entry,
@@ -2709,17 +2733,17 @@ static int
check_usage_backwards(struct task_struct *curr, struct held_lock *this,
enum lock_usage_bit bit, const char *irqclass)
{
- int ret;
+ enum bfs_result ret;
struct lock_list root;
struct lock_list *uninitialized_var(target_entry);

root.parent = NULL;
root.class = hlock_class(this);
ret = find_usage_backwards(&root, bit, &target_entry);
- if (ret < 0)
+ if (bfs_error(ret))
return print_bfs_bug(ret);
- if (ret == 1)
- return ret;
+ if (ret == BFS_RNOMATCH)
+ return 1;

return print_irq_inversion_bug(curr, &root, target_entry,
this, 0, irqclass);
--
2.14.1

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