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Message-Id: <20220211035526.1329503-2-longman@redhat.com>
Date: Thu, 10 Feb 2022 22:55:26 -0500
From: Waiman Long <longman@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Will Deacon <will.deacon@....com>,
Boqun Feng <boqun.feng@...il.com>
Cc: linux-kernel@...r.kernel.org, Waiman Long <longman@...hat.com>
Subject: [PATCH 2/2] locking/lockdep: Iterate lock_classes directly when reading lockdep files
When dumping lock_classes information via /proc/lockdep, we can't take
the lockdep lock as the lock hold time is indeterminate. Iterating
over all_lock_classes without holding lock can be dangerous as there
is a slight chance that it may branch off to other lists leading to
infinite loop or even access invalid memory if changes are made to
all_lock_classes list in parallel.
To avoid this problem, iteration of lock classes is now done directly
on the lock_classes array itself. The lock_classes_in_use bitmap is
checked to see if the lock class is being used. To avoid iterating
the full array all the times, a new max_lock_class_idx value is added
to track the maximum lock_class index that is currently being used.
We can theoretically take the lockdep lock for iterating all_lock_classes
when other lockdep files (lockdep_stats and lock_stat) are accessed as
the lock hold time will be shorter for them. For consistency, they are
also modified to iterate the lock_classes array directly.
Signed-off-by: Waiman Long <longman@...hat.com>
---
kernel/locking/lockdep.c | 14 +++++---
kernel/locking/lockdep_internals.h | 6 ++--
kernel/locking/lockdep_proc.c | 51 +++++++++++++++++++++++++-----
3 files changed, 56 insertions(+), 15 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 77bbe557d48b..7a9ce6d26285 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -183,11 +183,9 @@ static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);
static struct hlist_head lock_keys_hash[KEYHASH_SIZE];
unsigned long nr_lock_classes;
unsigned long nr_zapped_classes;
-#ifndef CONFIG_DEBUG_LOCKDEP
-static
-#endif
+unsigned long max_lock_class_idx;
struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
-static DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS);
+DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS);
static inline struct lock_class *hlock_class(struct held_lock *hlock)
{
@@ -338,7 +336,7 @@ static inline void lock_release_holdtime(struct held_lock *hlock)
* elements. These elements are linked together by the lock_entry member in
* struct lock_class.
*/
-LIST_HEAD(all_lock_classes);
+static LIST_HEAD(all_lock_classes);
static LIST_HEAD(free_lock_classes);
/**
@@ -1252,6 +1250,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
struct lockdep_subclass_key *key;
struct hlist_head *hash_head;
struct lock_class *class;
+ int idx;
DEBUG_LOCKS_WARN_ON(!irqs_disabled());
@@ -1317,6 +1316,9 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
* of classes.
*/
list_move_tail(&class->lock_entry, &all_lock_classes);
+ idx = class - lock_classes;
+ if (idx > max_lock_class_idx)
+ max_lock_class_idx = idx;
if (verbose(class)) {
graph_unlock();
@@ -5998,6 +6000,8 @@ static void zap_class(struct pending_free *pf, struct lock_class *class)
WRITE_ONCE(class->name, NULL);
nr_lock_classes--;
__clear_bit(class - lock_classes, lock_classes_in_use);
+ if (class - lock_classes == max_lock_class_idx)
+ max_lock_class_idx--;
} else {
WARN_ONCE(true, "%s() failed for class %s\n", __func__,
class->name);
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index ecb8662e7a4e..bbe9000260d0 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -121,7 +121,6 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
#define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5)
-extern struct list_head all_lock_classes;
extern struct lock_chain lock_chains[];
#define LOCK_USAGE_CHARS (2*XXX_LOCK_USAGE_STATES + 1)
@@ -151,6 +150,10 @@ extern unsigned int nr_large_chain_blocks;
extern unsigned int max_lockdep_depth;
extern unsigned int max_bfs_queue_depth;
+extern unsigned long max_lock_class_idx;
+
+extern struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
+extern unsigned long lock_classes_in_use[];
#ifdef CONFIG_PROVE_LOCKING
extern unsigned long lockdep_count_forward_deps(struct lock_class *);
@@ -205,7 +208,6 @@ struct lockdep_stats {
};
DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats);
-extern struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
#define __debug_atomic_inc(ptr) \
this_cpu_inc(lockdep_stats.ptr);
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index b8d9a050c337..15fdc7fa5c68 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -24,14 +24,33 @@
#include "lockdep_internals.h"
+/*
+ * Since iteration of lock_classes is done without holding the lockdep lock,
+ * it is not safe to iterate all_lock_classes list directly as the iteration
+ * may branch off to free_lock_classes or the zapped list. Iteration is done
+ * directly on the lock_classes array by checking the lock_classes_in_use
+ * bitmap and max_lock_class_idx.
+ */
+#define iterate_lock_classes(idx, class) \
+ for (idx = 0, class = lock_classes; idx <= max_lock_class_idx; \
+ idx++, class++)
+
static void *l_next(struct seq_file *m, void *v, loff_t *pos)
{
- return seq_list_next(v, &all_lock_classes, pos);
+ struct lock_class *class = v;
+
+ ++class;
+ *pos = class - lock_classes;
+ return (*pos > max_lock_class_idx) ? NULL : class;
}
static void *l_start(struct seq_file *m, loff_t *pos)
{
- return seq_list_start_head(&all_lock_classes, *pos);
+ unsigned long idx = *pos;
+
+ if (idx > max_lock_class_idx)
+ return NULL;
+ return lock_classes + idx;
}
static void l_stop(struct seq_file *m, void *v)
@@ -57,14 +76,16 @@ static void print_name(struct seq_file *m, struct lock_class *class)
static int l_show(struct seq_file *m, void *v)
{
- struct lock_class *class = list_entry(v, struct lock_class, lock_entry);
+ struct lock_class *class = v;
struct lock_list *entry;
char usage[LOCK_USAGE_CHARS];
+ int idx = class - lock_classes;
- if (v == &all_lock_classes) {
+ if (v == lock_classes)
seq_printf(m, "all lock classes:\n");
+
+ if (!test_bit(idx, lock_classes_in_use))
return 0;
- }
seq_printf(m, "%p", class->key);
#ifdef CONFIG_DEBUG_LOCKDEP
@@ -220,8 +241,11 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
#ifdef CONFIG_PROVE_LOCKING
struct lock_class *class;
+ unsigned long idx;
- list_for_each_entry(class, &all_lock_classes, lock_entry) {
+ iterate_lock_classes(idx, class) {
+ if (!test_bit(idx, lock_classes_in_use))
+ continue;
if (class->usage_mask == 0)
nr_unused++;
@@ -254,6 +278,7 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
sum_forward_deps += lockdep_count_forward_deps(class);
}
+
#ifdef CONFIG_DEBUG_LOCKDEP
DEBUG_LOCKS_WARN_ON(debug_atomic_read(nr_unused_locks) != nr_unused);
#endif
@@ -345,6 +370,8 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
seq_printf(m, " max bfs queue depth: %11u\n",
max_bfs_queue_depth);
#endif
+ seq_printf(m, " max lock class index: %11lu\n",
+ max_lock_class_idx);
lockdep_stats_debug_show(m);
seq_printf(m, " debug_locks: %11u\n",
debug_locks);
@@ -622,12 +649,16 @@ static int lock_stat_open(struct inode *inode, struct file *file)
if (!res) {
struct lock_stat_data *iter = data->stats;
struct seq_file *m = file->private_data;
+ unsigned long idx;
- list_for_each_entry(class, &all_lock_classes, lock_entry) {
+ iterate_lock_classes(idx, class) {
+ if (!test_bit(idx, lock_classes_in_use))
+ continue;
iter->class = class;
iter->stats = lock_stats(class);
iter++;
}
+
data->iter_end = iter;
sort(data->stats, data->iter_end - data->stats,
@@ -645,6 +676,7 @@ static ssize_t lock_stat_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
struct lock_class *class;
+ unsigned long idx;
char c;
if (count) {
@@ -654,8 +686,11 @@ static ssize_t lock_stat_write(struct file *file, const char __user *buf,
if (c != '0')
return count;
- list_for_each_entry(class, &all_lock_classes, lock_entry)
+ iterate_lock_classes(idx, class) {
+ if (!test_bit(idx, lock_classes_in_use))
+ continue;
clear_lock_stats(class);
+ }
}
return count;
}
--
2.27.0
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