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SubjectRe: [PATCH 3/3] audit: clean up refcounting in audit-tree
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On Fri, 2012-07-06 at 13:51 -0400, Eric Paris wrote:
> On Mon, 2012-06-25 at 19:46 +0200, Miklos Szeredi wrote:
> > From: Miklos Szeredi <mszeredi@suse.cz>
> >
> > Drop the initial reference by fsnotify_init_mark early instead of
> > audit_tree_freeing_mark() at destroy time.
> >
> > In the cases we destroy the mark before we drop the initial reference we need to
> > get rid of the get_mark that balances the put_mark in audit_tree_freeing_mark().
> >
> > Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
>
> I don't love this. The reference from fsnotify_init_mark() should live
> until fsnotify_mark_destroy(). If we need to drop a reference in
> audit_tree_freeing_mark() we should be taking that elsewhere....
>

There's no point in dropping a ref in ->freeing_mark, as the caller
needs to hold a ref anyways.


Thanks,
Miklos

> > ---
> > kernel/audit_tree.c | 12 +++++++++---
> > 1 files changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> > index 31fdc48..7b95706 100644
> > --- a/kernel/audit_tree.c
> > +++ b/kernel/audit_tree.c
> > @@ -292,6 +292,7 @@ static void untag_chunk(struct node *p)
> > spin_unlock(&hash_lock);
> > spin_unlock(&entry->lock);
> > fsnotify_destroy_mark(entry);
> > + fsnotify_put_mark(&new->mark); /* drop initial reference */
> > goto out;
> >
> > Fallback:
> > @@ -330,7 +331,6 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree)
> > spin_unlock(&hash_lock);
> > chunk->dead = 1;
> > spin_unlock(&entry->lock);
> > - fsnotify_get_mark(entry);
> > fsnotify_destroy_mark(entry);
> > fsnotify_put_mark(entry);
> > return 0;
> > @@ -346,6 +346,7 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree)
> > insert_hash(chunk);
> > spin_unlock(&hash_lock);
> > spin_unlock(&entry->lock);
> > + fsnotify_put_mark(entry); /* drop initial reference */
> > return 0;
> > }
> >
> > @@ -411,7 +412,6 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> > spin_unlock(&chunk_entry->lock);
> > spin_unlock(&old_entry->lock);
> >
> > - fsnotify_get_mark(chunk_entry);
> > fsnotify_destroy_mark(chunk_entry);
> >
> > fsnotify_put_mark(chunk_entry);
> > @@ -444,6 +444,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> > spin_unlock(&chunk_entry->lock);
> > spin_unlock(&old_entry->lock);
> > fsnotify_destroy_mark(old_entry);
> > + fsnotify_put_mark(chunk_entry); /* drop initial reference */
> > fsnotify_put_mark(old_entry); /* pair to fsnotify_find mark_entry */
> > return 0;
> > }
> > @@ -915,7 +916,12 @@ static void audit_tree_freeing_mark(struct fsnotify_mark *entry, struct fsnotify
> > struct audit_chunk *chunk = container_of(entry, struct audit_chunk, mark);
> >
> > evict_chunk(chunk);
> > - fsnotify_put_mark(entry);
> > +
> > + /*
> > + * We are guaranteed to have at least one reference to the mark from
> > + * either the inode or the caller of fsnotify_destroy_mark().
> > + */
> > + BUG_ON(atomic_read(&entry->refcnt) < 1);
> > }
> >
> > static bool audit_tree_send_event(struct fsnotify_group *group, struct inode *inode,
>
>




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