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

Paul Moore
2018-11-06T13:58:54Z

On Thu, Oct 18, 2018 at 3:27 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> 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().

Yeah, I wasn't expecting to see that, maybe it will make sense as I
work through the rest of the patchset.

Jan, can you explain the reason behind the change? I'm a little
nervous that this is simply hiding a problem (e.g. the list_empty()
check in splice).

> 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

--
paul moore