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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 <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-4-boqun.feng@gmail.com
This commit is contained in:
Boqun Feng 2020-08-07 15:42:22 +08:00 committed by Peter Zijlstra
parent 224ec489d3
commit b11be024de
1 changed files with 89 additions and 66 deletions
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155
kernel/locking/lockdep.c
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@ -1471,28 +1471,58 @@ static inline struct list_head *get_dep_list(struct lock_list *lock, int offset)
return lock_class + 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 * Forward- or backward-dependency search, used for both circular dependency
* checking and hardirq-unsafe/softirq-unsafe checking. * checking and hardirq-unsafe/softirq-unsafe checking.
*/ */
static int __bfs(struct lock_list *source_entry, static enum bfs_result __bfs(struct lock_list *source_entry,
void *data, void *data,
int (*match)(struct lock_list *entry, void *data), int (*match)(struct lock_list *entry, void *data),
struct lock_list **target_entry, struct lock_list **target_entry,
int offset) int offset)
{ {
struct lock_list *entry; struct lock_list *entry;
struct lock_list *lock; struct lock_list *lock;
struct list_head *head; struct list_head *head;
struct circular_queue *cq = &lock_cq; struct circular_queue *cq = &lock_cq;
int ret = 1; enum bfs_result ret = BFS_RNOMATCH;
lockdep_assert_locked(); lockdep_assert_locked();
if (match(source_entry, data)) { if (match(source_entry, data)) {
*target_entry = source_entry; *target_entry = source_entry;
ret = 0; ret = BFS_RMATCH;
goto exit; goto exit;
} }
@ -1506,7 +1536,7 @@ static int __bfs(struct lock_list *source_entry,
while ((lock = __cq_dequeue(cq))) { while ((lock = __cq_dequeue(cq))) {
if (!lock->class) { if (!lock->class) {
ret = -2; ret = BFS_EINVALIDNODE;
goto exit; goto exit;
} }
@ -1518,12 +1548,12 @@ static int __bfs(struct lock_list *source_entry,
mark_lock_accessed(entry, lock); mark_lock_accessed(entry, lock);
if (match(entry, data)) { if (match(entry, data)) {
*target_entry = entry; *target_entry = entry;
ret = 0; ret = BFS_RMATCH;
goto exit; goto exit;
} }
if (__cq_enqueue(cq, entry)) { if (__cq_enqueue(cq, entry)) {
ret = -1; ret = BFS_EQUEUEFULL;
goto exit; goto exit;
} }
cq_depth = __cq_get_elem_count(cq); cq_depth = __cq_get_elem_count(cq);
@ -1536,20 +1566,22 @@ static int __bfs(struct lock_list *source_entry,
return ret; return ret;
} }
static inline int __bfs_forwards(struct lock_list *src_entry, static inline enum bfs_result
void *data, __bfs_forwards(struct lock_list *src_entry,
int (*match)(struct lock_list *entry, void *data), void *data,
struct lock_list **target_entry) int (*match)(struct lock_list *entry, void *data),
struct lock_list **target_entry)
{ {
return __bfs(src_entry, data, match, target_entry, return __bfs(src_entry, data, match, target_entry,
offsetof(struct lock_class, locks_after)); offsetof(struct lock_class, locks_after));
} }
static inline int __bfs_backwards(struct lock_list *src_entry, static inline enum bfs_result
void *data, __bfs_backwards(struct lock_list *src_entry,
int (*match)(struct lock_list *entry, void *data), void *data,
struct lock_list **target_entry) int (*match)(struct lock_list *entry, void *data),
struct lock_list **target_entry)
{ {
return __bfs(src_entry, data, match, target_entry, return __bfs(src_entry, data, match, target_entry,
offsetof(struct lock_class, locks_before)); 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 * 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, check_path(struct lock_class *target, struct lock_list *src_entry,
struct lock_list **target_entry) struct lock_list **target_entry)
{ {
int ret; enum bfs_result ret;
ret = __bfs_forwards(src_entry, (void *)target, class_equal, ret = __bfs_forwards(src_entry, (void *)target, class_equal,
target_entry); target_entry);
if (unlikely(ret < 0)) if (unlikely(bfs_error(ret)))
print_bfs_bug(ret); print_bfs_bug(ret);
return 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 * lead to <target>. If it can, there is a circle when adding
* <target> -> <src> dependency. * <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, check_noncircular(struct held_lock *src, struct held_lock *target,
struct lock_trace **const trace) struct lock_trace **const trace)
{ {
int ret; enum bfs_result ret;
struct lock_list *target_entry; struct lock_list *target_entry;
struct lock_list src_entry = { struct lock_list src_entry = {
.class = hlock_class(src), .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); ret = check_path(hlock_class(target), &src_entry, &target_entry);
if (unlikely(!ret)) { if (unlikely(ret == BFS_RMATCH)) {
if (!*trace) { if (!*trace) {
/* /*
* If save_trace fails here, the printing might * 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 * <target> or not. If it can, <src> -> <target> dependency is already
* in the graph. * 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) check_redundant(struct held_lock *src, struct held_lock *target)
{ {
int ret; enum bfs_result ret;
struct lock_list *target_entry; struct lock_list *target_entry;
struct lock_list src_entry = { struct lock_list src_entry = {
.class = hlock_class(src), .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); ret = check_path(hlock_class(target), &src_entry, &target_entry);
if (!ret) { if (ret == BFS_RMATCH)
debug_atomic_inc(nr_redundant); debug_atomic_inc(nr_redundant);
ret = 2;
} else if (ret < 0)
ret = 0;
return ret; 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 * Find a node in the forwards-direction dependency sub-graph starting
* at @root->class that matches @bit. * 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. * 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, find_usage_forwards(struct lock_list *root, unsigned long usage_mask,
struct lock_list **target_entry) struct lock_list **target_entry)
{ {
int result; enum bfs_result result;
debug_atomic_inc(nr_find_usage_forwards_checks); 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 * Find a node in the backwards-direction dependency sub-graph starting
* at @root->class that matches @bit. * 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, find_usage_backwards(struct lock_list *root, unsigned long usage_mask,
struct lock_list **target_entry) struct lock_list **target_entry)
{ {
int result; enum bfs_result result;
debug_atomic_inc(nr_find_usage_backwards_checks); 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 *target_entry1; struct lock_list *target_entry1;
struct lock_list *target_entry; struct lock_list *target_entry;
struct lock_list this, that; struct lock_list this, that;
int ret; enum bfs_result ret;
/* /*
* Step 1: gather all hard/soft IRQs usages backward in an * 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); this.class = hlock_class(prev);
ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, NULL); ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, NULL);
if (ret < 0) { if (bfs_error(ret)) {
print_bfs_bug(ret); print_bfs_bug(ret);
return 0; return 0;
} }
@ -2276,12 +2297,12 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
that.class = hlock_class(next); that.class = hlock_class(next);
ret = find_usage_forwards(&that, forward_mask, &target_entry1); ret = find_usage_forwards(&that, forward_mask, &target_entry1);
if (ret < 0) { if (bfs_error(ret)) {
print_bfs_bug(ret); print_bfs_bug(ret);
return 0; return 0;
} }
if (ret == 1) if (ret == BFS_RNOMATCH)
return ret; return 1;
/* /*
* Step 3: we found a bad match! Now retrieve a lock from the backward * 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); backward_mask = original_mask(target_entry1->class->usage_mask);
ret = find_usage_backwards(&this, backward_mask, &target_entry); ret = find_usage_backwards(&this, backward_mask, &target_entry);
if (ret < 0) { if (bfs_error(ret)) {
print_bfs_bug(ret); print_bfs_bug(ret);
return 0; return 0;
} }
if (DEBUG_LOCKS_WARN_ON(ret == 1)) if (DEBUG_LOCKS_WARN_ON(ret == BFS_RNOMATCH))
return 1; return 1;
/* /*
@ -2463,7 +2484,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
struct lock_trace **const trace) struct lock_trace **const trace)
{ {
struct lock_list *entry; struct lock_list *entry;
int ret; enum bfs_result ret;
if (!hlock_class(prev)->key || !hlock_class(next)->key) { 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. * in the graph whose neighbours are to be checked.
*/ */
ret = check_noncircular(next, prev, trace); ret = check_noncircular(next, prev, trace);
if (unlikely(ret <= 0)) if (unlikely(bfs_error(ret) || ret == BFS_RMATCH))
return 0; return 0;
if (!check_irq_usage(curr, prev, next)) 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? * Is the <prev> -> <next> link redundant?
*/ */
ret = check_redundant(prev, next); ret = check_redundant(prev, next);
if (ret != 1) if (bfs_error(ret))
return ret; return 0;
else if (ret == BFS_RMATCH)
return 2;
#endif #endif
if (!*trace) { if (!*trace) {
@ -3436,19 +3459,19 @@ static int
check_usage_forwards(struct task_struct *curr, struct held_lock *this, check_usage_forwards(struct task_struct *curr, struct held_lock *this,
enum lock_usage_bit bit, const char *irqclass) enum lock_usage_bit bit, const char *irqclass)
{ {
int ret; enum bfs_result ret;
struct lock_list root; struct lock_list root;
struct lock_list *target_entry; struct lock_list *target_entry;
root.parent = NULL; root.parent = NULL;
root.class = hlock_class(this); root.class = hlock_class(this);
ret = find_usage_forwards(&root, lock_flag(bit), &target_entry); ret = find_usage_forwards(&root, lock_flag(bit), &target_entry);
if (ret < 0) { if (bfs_error(ret)) {
print_bfs_bug(ret); print_bfs_bug(ret);
return 0; return 0;
} }
if (ret == 1) if (ret == BFS_RNOMATCH)
return ret; return 1;
print_irq_inversion_bug(curr, &root, target_entry, print_irq_inversion_bug(curr, &root, target_entry,
this, 1, irqclass); this, 1, irqclass);
@ -3463,19 +3486,19 @@ static int
check_usage_backwards(struct task_struct *curr, struct held_lock *this, check_usage_backwards(struct task_struct *curr, struct held_lock *this,
enum lock_usage_bit bit, const char *irqclass) enum lock_usage_bit bit, const char *irqclass)
{ {
int ret; enum bfs_result ret;
struct lock_list root; struct lock_list root;
struct lock_list *target_entry; struct lock_list *target_entry;
root.parent = NULL; root.parent = NULL;
root.class = hlock_class(this); root.class = hlock_class(this);
ret = find_usage_backwards(&root, lock_flag(bit), &target_entry); ret = find_usage_backwards(&root, lock_flag(bit), &target_entry);
if (ret < 0) { if (bfs_error(ret)) {
print_bfs_bug(ret); print_bfs_bug(ret);
return 0; return 0;
} }
if (ret == 1) if (ret == BFS_RNOMATCH)
return ret; return 1;
print_irq_inversion_bug(curr, &root, target_entry, print_irq_inversion_bug(curr, &root, target_entry,
this, 0, irqclass); this, 0, irqclass);