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lockdep: Demagic the return value of BFS
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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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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@fbq
fbq authored and Peter Zijlstra committed Aug 26, 2020
1 parent 224ec48 commit b11be02
Showing 1 changed file with 89 additions and 66 deletions.
155 changes: 89 additions & 66 deletions kernel/locking/lockdep.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
}

Expand All @@ -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;
}

Expand All @@ -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);
Expand All @@ -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));
Expand Down Expand Up @@ -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;
Expand All @@ -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 *target_entry;
struct lock_list src_entry = {
.class = hlock_class(src),
Expand All @@ -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
Expand All @@ -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 *target_entry;
struct lock_list src_entry = {
.class = hlock_class(src),
Expand All @@ -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;
}
Expand Down Expand Up @@ -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);

Expand All @@ -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);

Expand Down Expand Up @@ -2247,7 +2268,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
struct lock_list *target_entry1;
struct lock_list *target_entry;
struct lock_list this, that;
int ret;
enum bfs_result ret;

/*
* Step 1: gather all hard/soft IRQs usages backward in an
Expand All @@ -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;
}
Expand All @@ -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
Expand All @@ -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;

/*
Expand Down Expand Up @@ -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) {
/*
Expand Down Expand Up @@ -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))
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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 *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);
Expand All @@ -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 *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);
Expand Down

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