[RFC v7 03/19] lockdep: Demagic the return value of BFS
From: Boqun Feng
Date: Fri Aug 07 2020 - 03:43:28 EST
__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 | 155 ++++++++++++++++++++++-----------------
1 file changed, 89 insertions(+), 66 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index fbcbb6350ce7..8fba156db5ba 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1471,28 +1471,58 @@ static inline struct list_head *get_dep_list(struct lock_list *lock, int offset)
return lock_class + offset;
}
+/*
+ * 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;
+}
/*
* Forward- or backward-dependency search, used for both circular dependency
* checking and hardirq-unsafe/softirq-unsafe checking.
*/
-static int __bfs(struct lock_list *source_entry,
- void *data,
- int (*match)(struct lock_list *entry, void *data),
- struct lock_list **target_entry,
- int offset)
+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 offset)
{
struct lock_list *entry;
struct lock_list *lock;
struct list_head *head;
struct circular_queue *cq = &lock_cq;
- int ret = 1;
+ enum bfs_result ret = BFS_RNOMATCH;
lockdep_assert_locked();
if (match(source_entry, data)) {
*target_entry = source_entry;
- ret = 0;
+ ret = BFS_RMATCH;
goto exit;
}
@@ -1506,7 +1536,7 @@ static int __bfs(struct lock_list *source_entry,
while ((lock = __cq_dequeue(cq))) {
if (!lock->class) {
- ret = -2;
+ ret = BFS_EINVALIDNODE;
goto exit;
}
@@ -1518,12 +1548,12 @@ 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, entry)) {
- ret = -1;
+ ret = BFS_EQUEUEFULL;
goto exit;
}
cq_depth = __cq_get_elem_count(cq);
@@ -1536,20 +1566,22 @@ 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,
offsetof(struct lock_class, locks_after));
}
-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,
offsetof(struct lock_class, locks_before));
@@ -1775,18 +1807,18 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
/*
* Check that the dependency graph starting at <src> can lead to
- * <target> or not. Print an error and return 0 if it does.
+ * <target> or not.
*/
-static noinline int
+static noinline enum bfs_result
check_path(struct lock_class *target, struct lock_list *src_entry,
struct lock_list **target_entry)
{
- int ret;
+ enum bfs_result ret;
ret = __bfs_forwards(src_entry, (void *)target, class_equal,
target_entry);
- if (unlikely(ret < 0))
+ if (unlikely(bfs_error(ret)))
print_bfs_bug(ret);
return ret;
@@ -1797,13 +1829,13 @@ check_path(struct lock_class *target, struct lock_list *src_entry,
* lead to <target>. If it can, there is a circle when adding
* <target> -> <src> dependency.
*
- * Print an error and return 0 if it does.
+ * Print an error and return BFS_RMATCH if it does.
*/
-static noinline int
+static noinline enum bfs_result
check_noncircular(struct held_lock *src, struct held_lock *target,
struct lock_trace **const trace)
{
- int ret;
+ enum bfs_result ret;
struct lock_list *uninitialized_var(target_entry);
struct lock_list src_entry = {
.class = hlock_class(src),
@@ -1814,7 +1846,7 @@ check_noncircular(struct held_lock *src, struct held_lock *target,
ret = check_path(hlock_class(target), &src_entry, &target_entry);
- if (unlikely(!ret)) {
+ if (unlikely(ret == BFS_RMATCH)) {
if (!*trace) {
/*
* If save_trace fails here, the printing might
@@ -1836,12 +1868,13 @@ check_noncircular(struct held_lock *src, struct held_lock *target,
* <target> or not. If it can, <src> -> <target> dependency is already
* in the graph.
*
- * Print an error and return 2 if it does or 1 if it does not.
+ * Return BFS_RMATCH if it does, or BFS_RMATCH if it does not, return BFS_E* if
+ * any error appears in the bfs search.
*/
-static noinline int
+static noinline enum bfs_result
check_redundant(struct held_lock *src, struct held_lock *target)
{
- int ret;
+ enum bfs_result ret;
struct lock_list *uninitialized_var(target_entry);
struct lock_list src_entry = {
.class = hlock_class(src),
@@ -1852,11 +1885,8 @@ check_redundant(struct held_lock *src, struct held_lock *target)
ret = check_path(hlock_class(target), &src_entry, &target_entry);
- if (!ret) {
+ if (ret == BFS_RMATCH)
debug_atomic_inc(nr_redundant);
- ret = 2;
- } else if (ret < 0)
- ret = 0;
return ret;
}
@@ -1886,17 +1916,14 @@ static inline int usage_match(struct lock_list *entry, void *mask)
* Find a node in the forwards-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
+ * Return BFS_MATCH 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, unsigned long usage_mask,
struct lock_list **target_entry)
{
- int result;
+ enum bfs_result result;
debug_atomic_inc(nr_find_usage_forwards_checks);
@@ -1908,18 +1935,12 @@ find_usage_forwards(struct lock_list *root, unsigned long usage_mask,
/*
* 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, unsigned long usage_mask,
struct lock_list **target_entry)
{
- int result;
+ enum bfs_result result;
debug_atomic_inc(nr_find_usage_backwards_checks);
@@ -2247,7 +2268,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
struct lock_list *uninitialized_var(target_entry1);
struct lock_list *uninitialized_var(target_entry);
struct lock_list this, that;
- int ret;
+ enum bfs_result ret;
/*
* Step 1: gather all hard/soft IRQs usages backward in an
@@ -2257,7 +2278,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
this.class = hlock_class(prev);
ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, NULL);
- if (ret < 0) {
+ if (bfs_error(ret)) {
print_bfs_bug(ret);
return 0;
}
@@ -2276,12 +2297,12 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
that.class = hlock_class(next);
ret = find_usage_forwards(&that, forward_mask, &target_entry1);
- if (ret < 0) {
+ if (bfs_error(ret)) {
print_bfs_bug(ret);
return 0;
}
- if (ret == 1)
- return ret;
+ if (ret == BFS_RNOMATCH)
+ return 1;
/*
* Step 3: we found a bad match! Now retrieve a lock from the backward
@@ -2291,11 +2312,11 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
backward_mask = original_mask(target_entry1->class->usage_mask);
ret = find_usage_backwards(&this, backward_mask, &target_entry);
- if (ret < 0) {
+ if (bfs_error(ret)) {
print_bfs_bug(ret);
return 0;
}
- if (DEBUG_LOCKS_WARN_ON(ret == 1))
+ if (DEBUG_LOCKS_WARN_ON(ret == BFS_RNOMATCH))
return 1;
/*
@@ -2463,7 +2484,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
struct lock_trace **const trace)
{
struct lock_list *entry;
- int ret;
+ enum bfs_result ret;
if (!hlock_class(prev)->key || !hlock_class(next)->key) {
/*
@@ -2494,7 +2515,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
* in the graph whose neighbours are to be checked.
*/
ret = check_noncircular(next, prev, trace);
- if (unlikely(ret <= 0))
+ if (unlikely(bfs_error(ret) || ret == BFS_RMATCH))
return 0;
if (!check_irq_usage(curr, prev, next))
@@ -2531,8 +2552,10 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
* Is the <prev> -> <next> link redundant?
*/
ret = check_redundant(prev, next);
- if (ret != 1)
- return ret;
+ if (bfs_error(ret))
+ return 0;
+ else if (ret == BFS_RMATCH)
+ return 2;
#endif
if (!*trace) {
@@ -3436,19 +3459,19 @@ 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, lock_flag(bit), &target_entry);
- if (ret < 0) {
+ if (bfs_error(ret)) {
print_bfs_bug(ret);
return 0;
}
- if (ret == 1)
- return ret;
+ if (ret == BFS_RNOMATCH)
+ return 1;
print_irq_inversion_bug(curr, &root, target_entry,
this, 1, irqclass);
@@ -3463,19 +3486,19 @@ 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, lock_flag(bit), &target_entry);
- if (ret < 0) {
+ if (bfs_error(ret)) {
print_bfs_bug(ret);
return 0;
}
- if (ret == 1)
- return ret;
+ if (ret == BFS_RNOMATCH)
+ return 1;
print_irq_inversion_bug(curr, &root, target_entry,
this, 0, irqclass);
--
2.28.0