Re: [PATCH 1/4] lockdep: lock_set_subclass() fix

[Tejun Heo <tj@kernel.org>]

Hello,

On Mon, Nov 07, 2011 at 05:10:29PM +0100, Peter Zijlstra wrote:
> We could move the key and name pointer to the start of the structure and
> memset everything after that, however wouldn't that leave kmemcheck with
> the same problem? It wouldn't know those two pointers would be
> initialized properly.

At that point, lockdep_map is guaranteed to have passed through
lockdep_init_map(), so I think it should be fine.

> @@ -148,9 +148,9 @@ void clear_lock_stats(struct lock_class *class);
>   * This is embedded into specific lock instances:
>   */
>  struct lockdep_map {
> +	const char			*name;
>  	struct lock_class_key		*key;
>  	struct lock_class		*class_cache[NR_LOCKDEP_CACHING_CLASSES];
> -	const char			*name;
>  #ifdef CONFIG_LOCK_STAT
>  	int				cpu;
>  	unsigned long			ip;

Probably fat comment explaining the ordering requirement here w/

#define LOCKDEP_MAP_INIT_OFFSET		offsetof(struct lockdep_map, class_cache)

> diff --git a/kernel/lockdep.c b/kernel/lockdep.c
> index e69434b..81855cf 100644
> --- a/kernel/lockdep.c
> +++ b/kernel/lockdep.c
> @@ -2948,7 +2948,8 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
>  void lockdep_init_map(struct lockdep_map *lock, const char *name,
>  		      struct lock_class_key *key, int subclass)
>  {
> -	memset(lock, 0, sizeof(*lock));
> +	kmemcheck_mark_initialized(lock, 2*sizeof(void *));
> +	memset(&lock->class_cache[0], 0, sizeof(*lock)-2*sizeof(void *));

And something like the following?

	memset((void *)lock + LOCKDEP_MAP_INIT_OFFSET, 0,
		sizeof(*lock) - LOCKDEP_MAP_INIT_OFFSET);

Thanks.

-- 
tejun