Re: [PATCH 06/14] audit: Factor out chunk replacement code

Richard Guy Briggs
2018-10-18T19:27:01Z

On 2018-10-17 12:14, Jan Kara wrote:
> Chunk replacement code is very similar for the cases where we grow or
> shrink chunk. Factor the code out into a common helper function.

Noting just the switch from list_replace_init() to list_splice_init().

Reviewed-by: Richard Guy Briggs <rgb@redhat.com>

> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> kernel/audit_tree.c | 86 +++++++++++++++++++++++++----------------------------
> 1 file changed, 40 insertions(+), 46 deletions(-)
>
> diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> index 307749d6773c..d8f6cfa0005b 100644
> --- a/kernel/audit_tree.c
> +++ b/kernel/audit_tree.c
> @@ -235,6 +235,38 @@ static struct audit_chunk *find_chunk(struct node *p)
> return container_of(p, struct audit_chunk, owners[0]);
> }
>
> +static void replace_chunk(struct audit_chunk *new, struct audit_chunk *old,
> + struct node *skip)
> +{
> + struct audit_tree *owner;
> + int i, j;
> +
> + new->key = old->key;
> + list_splice_init(&old->trees, &new->trees);
> + list_for_each_entry(owner, &new->trees, same_root)
> + owner->root = new;
> + for (i = j = 0; j < old->count; i++, j++) {
> + if (&old->owners[j] == skip) {
> + i--;
> + continue;
> + }
> + owner = old->owners[j].owner;
> + new->owners[i].owner = owner;
> + new->owners[i].index = old->owners[j].index - j + i;
> + if (!owner) /* result of earlier fallback */
> + continue;
> + get_tree(owner);
> + list_replace_init(&old->owners[j].list, &new->owners[i].list);
> + }
> + /*
> + * Make sure chunk is fully initialized before making it visible in the
> + * hash. Pairs with a data dependency barrier in READ_ONCE() in
> + * audit_tree_lookup().
> + */
> + smp_wmb();
> + list_replace_rcu(&old->hash, &new->hash);
> +}
> +
> static void untag_chunk(struct node *p)
> {
> struct audit_chunk *chunk = find_chunk(p);
> @@ -242,7 +274,6 @@ static void untag_chunk(struct node *p)
> struct audit_chunk *new = NULL;
> struct audit_tree *owner;
> int size = chunk->count - 1;
> - int i, j;
>
> fsnotify_get_mark(entry);
>
> @@ -291,38 +322,16 @@ static void untag_chunk(struct node *p)
>
> chunk->dead = 1;
> spin_lock(&hash_lock);
> - new->key = chunk->key;
> - list_replace_init(&chunk->trees, &new->trees);
> if (owner->root == chunk) {
> list_del_init(&owner->same_root);
> owner->root = NULL;
> }
> -
> - for (i = j = 0; j <= size; i++, j++) {
> - struct audit_tree *s;
> - if (&chunk->owners[j] == p) {
> - list_del_init(&p->list);
> - i--;
> - continue;
> - }
> - s = chunk->owners[j].owner;
> - new->owners[i].owner = s;
> - new->owners[i].index = chunk->owners[j].index - j + i;
> - if (!s) /* result of earlier fallback */
> - continue;
> - get_tree(s);
> - list_replace_init(&chunk->owners[j].list, &new->owners[i].list);
> - }
> -
> - list_for_each_entry(owner, &new->trees, same_root)
> - owner->root = new;
> + list_del_init(&p->list);
> /*
> - * Make sure chunk is fully initialized before making it visible in the
> - * hash. Pairs with a data dependency barrier in READ_ONCE() in
> - * audit_tree_lookup().
> + * This has to go last when updating chunk as once replace_chunk() is
> + * called, new RCU readers can see the new chunk.
> */
> - smp_wmb();
> - list_replace_rcu(&chunk->hash, &new->hash);
> + replace_chunk(new, chunk, p);
> spin_unlock(&hash_lock);
> fsnotify_detach_mark(entry);
> mutex_unlock(&entry->group->mark_mutex);
> @@ -399,7 +408,6 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree)
> static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> {
> struct fsnotify_mark *old_entry, *chunk_entry;
> - struct audit_tree *owner;
> struct audit_chunk *chunk, *old;
> struct node *p;
> int n;
> @@ -464,35 +472,21 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> fsnotify_put_mark(old_entry);
> return 0;
> }
> - chunk->key = old->key;
> - list_replace_init(&old->trees, &chunk->trees);
> - for (n = 0, p = chunk->owners; n < old->count; n++, p++) {
> - struct audit_tree *s = old->owners[n].owner;
> - p->owner = s;
> - p->index = old->owners[n].index;
> - if (!s) /* result of fallback in untag */
> - continue;
> - get_tree(s);
> - list_replace_init(&old->owners[n].list, &p->list);
> - }
> + p = &chunk->owners[chunk->count - 1];
> p->index = (chunk->count - 1) | (1U<<31);
> p->owner = tree;
> get_tree(tree);
> list_add(&p->list, &tree->chunks);
> - list_for_each_entry(owner, &chunk->trees, same_root)
> - owner->root = chunk;
> old->dead = 1;
> if (!tree->root) {
> tree->root = chunk;
> list_add(&tree->same_root, &chunk->trees);
> }
> /*
> - * Make sure chunk is fully initialized before making it visible in the
> - * hash. Pairs with a data dependency barrier in READ_ONCE() in
> - * audit_tree_lookup().
> + * This has to go last when updating chunk as once replace_chunk() is
> + * called, new RCU readers can see the new chunk.
> */
> - smp_wmb();
> - list_replace_rcu(&old->hash, &chunk->hash);
> + replace_chunk(chunk, old, NULL);
> spin_unlock(&hash_lock);
> fsnotify_detach_mark(old_entry);
> mutex_unlock(&audit_tree_group->mark_mutex);
> --
> 2.16.4
>

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635