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Subject[PATCH v6 09/16] locking/lockdep: Reuse list entries that are no longer in use
Date
Instead of abandoning elements of list_entries[] that are no longer in
use, make alloc_list_entry() reuse array elements that have been freed.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
kernel/locking/lockdep.c | 48 +++++++++++++++++++++++++++++++---------
1 file changed, 38 insertions(+), 10 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 5b142f699503..5e8a3a17bb94 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -45,6 +45,7 @@
#include <linux/hash.h>
#include <linux/ftrace.h>
#include <linux/stringify.h>
+#include <linux/bitmap.h>
#include <linux/bitops.h>
#include <linux/gfp.h>
#include <linux/random.h>
@@ -132,6 +133,7 @@ static inline int debug_locks_off_graph_unlock(void)

unsigned long nr_list_entries;
static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];
+static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);

/*
* All data structures here are protected by the global debug_lock.
@@ -296,6 +298,7 @@ static struct pending_free {
struct list_head zapped_classes;
struct rcu_head rcu_head;
bool scheduled;
+ DECLARE_BITMAP(list_entries_being_freed, MAX_LOCKDEP_ENTRIES);
} pending_free[2];
static DECLARE_WAIT_QUEUE_HEAD(rcu_cb);

@@ -756,6 +759,19 @@ static bool assign_lock_key(struct lockdep_map *lock)
return true;
}

+static bool list_entry_being_freed(int list_entry_idx)
+{
+ struct pending_free *pf;
+ int i;
+
+ for (i = 0, pf = pending_free; i < ARRAY_SIZE(pending_free);
+ i++, pf++)
+ if (test_bit(list_entry_idx, pf->list_entries_being_freed))
+ return true;
+
+ return false;
+}
+
/*
* Initialize the lock_classes[] array elements, the free_lock_classes list
* and also the pending_free[] array.
@@ -896,7 +912,10 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
*/
static struct lock_list *alloc_list_entry(void)
{
- if (nr_list_entries >= MAX_LOCKDEP_ENTRIES) {
+ int idx = find_first_zero_bit(list_entries_in_use,
+ ARRAY_SIZE(list_entries));
+
+ if (idx >= ARRAY_SIZE(list_entries)) {
if (!debug_locks_off_graph_unlock())
return NULL;

@@ -904,7 +923,9 @@ static struct lock_list *alloc_list_entry(void)
dump_stack();
return NULL;
}
- return list_entries + nr_list_entries++;
+ nr_list_entries++;
+ __set_bit(idx, list_entries_in_use);
+ return list_entries + idx;
}

/*
@@ -1008,7 +1029,7 @@ static inline void mark_lock_accessed(struct lock_list *lock,
unsigned long nr;

nr = lock - list_entries;
- WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
+ WARN_ON(nr >= ARRAY_SIZE(list_entries)); /* Out-of-bounds, input fail */
lock->parent = parent;
lock->class->dep_gen_id = lockdep_dependency_gen_id;
}
@@ -1018,7 +1039,7 @@ static inline unsigned long lock_accessed(struct lock_list *lock)
unsigned long nr;

nr = lock - list_entries;
- WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
+ WARN_ON(nr >= ARRAY_SIZE(list_entries)); /* Out-of-bounds, input fail */
return lock->class->dep_gen_id == lockdep_dependency_gen_id;
}

@@ -4277,13 +4298,15 @@ static void zap_class(struct pending_free *pf, struct lock_class *class)
* Remove all dependencies this lock is
* involved in:
*/
- for (i = 0, entry = list_entries; i < nr_list_entries; i++, entry++) {
+ for_each_set_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) {
+ entry = list_entries + i;
if (entry->class != class && entry->links_to != class)
continue;
+ if (list_entry_being_freed(i))
+ continue;
+ set_bit(i, pf->list_entries_being_freed);
+ nr_list_entries--;
list_del_rcu(&entry->entry);
- /* Clear .class and .links_to to avoid double removal. */
- WRITE_ONCE(entry->class, NULL);
- WRITE_ONCE(entry->links_to, NULL);
}
if (list_empty(&class->locks_after) &&
list_empty(&class->locks_before)) {
@@ -4325,8 +4348,9 @@ static bool inside_selftest(void)
}

/*
- * Free all lock classes that are on the pf->zapped_classes list. May be called
- * from RCU callback context.
+ * Free all lock classes that are on the pf->zapped_classes list and also all
+ * list entries that have been marked as being freed. May be called from RCU
+ * callback context.
*/
static void free_zapped_classes(struct rcu_head *ch)
{
@@ -4342,6 +4366,9 @@ static void free_zapped_classes(struct rcu_head *ch)
reinit_class(class);
}
list_splice_init(&pf->zapped_classes, &free_lock_classes);
+ bitmap_andnot(list_entries_in_use, list_entries_in_use,
+ pf->list_entries_being_freed, ARRAY_SIZE(list_entries));
+ bitmap_clear(pf->list_entries_being_freed, 0, ARRAY_SIZE(list_entries));
graph_unlock();
restore_irqs:
raw_local_irq_restore(flags);
@@ -4626,6 +4653,7 @@ void __init lockdep_init(void)

printk(" memory used by lock dependency info: %zu kB\n",
(sizeof(list_entries) +
+ sizeof(list_entries_in_use) +
sizeof(lock_classes) +
sizeof(classhash_table) +
sizeof(chainhash_table) +
--
2.20.1.97.g81188d93c3-goog
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