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


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