On Tue, Jun 02, 2015 at 11:54:13AM +0200, Jerome Marchand wrote:
>
> I guess I jumped to conclusion here and my explanation is wrong. However
> there is still a bug which occurs when the kernel tries to access
> class->name is seq_stats:
>
> [ 43.533732] BUG: unable to handle kernel paging request at
> ffffffffa03181ce
> [ 43.534006] IP: [<ffffffff8142b489>] strnlen+0x9/0x50
Does something like so cure things?
---
kernel/locking/lockdep.c | 3 ++-
kernel/locking/lockdep_proc.c | 22 +++++++++++++++++-----
2 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index a0831e1b99f4..50ed2685f937 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3900,7 +3900,8 @@ static void zap_class(struct lock_class *class)
list_del_rcu(&class->hash_entry);
list_del_rcu(&class->lock_entry);
- class->key = NULL;
+ WRITE_ONCE(class->key, NULL);
+ WRITE_ONCE(class->name, NULL);
}
static inline int within(const void *addr, void *start, unsigned long size)
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index ef43ac4bafb5..03946779eacc 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -426,10 +426,12 @@ static void seq_lock_time(struct seq_file *m, struct
lock_time *lt)
static void seq_stats(struct seq_file *m, struct lock_stat_data *data)
{
- char name[39];
- struct lock_class *class;
+ struct lockdep_subclass_key *ckey;
struct lock_class_stats *stats;
+ struct lock_class *class;
int i, namelen;
+ char name[39];
+ char *cname;
class = data->class;
stats = &data->stats;
@@ -440,15 +442,25 @@ static void seq_stats(struct seq_file *m, struct
lock_stat_data *data)
if (class->subclass)
namelen -= 2;
- if (!class->name) {
+ rcu_read_lock_sched();
+ cname = rcu_dereference_sched(class->name);
+ ckey = rcu_dereference_sched(class->key);
+
+ if (!cname && !ckey) {
+ rcu_read_unlock_sched();
+ return;
+
+ } else if (!cname) {
char str[KSYM_NAME_LEN];
const char *key_name;
- key_name = __get_key_name(class->key, str);
+ key_name = __get_key_name(ckey, str);
snprintf(name, namelen, "%s", key_name);
} else {
- snprintf(name, namelen, "%s", class->name);
+ snprintf(name, namelen, "%s", cname);
}
+ rcu_read_unlock_sched();
+
namelen = strlen(name);
if (class->name_version > 1) {
snprintf(name+namelen, 3, "#%d", class->name_version);
--
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