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SubjectRe: [PATCH 01/15] kmemleak: Add the base support
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On Fri, 2008-12-12 at 00:01 +0200, Pekka Enberg wrote:
> On Wed, Dec 10, 2008 at 8:26 PM, Catalin Marinas
> <catalin.marinas@arm.com> wrote:
> > +static void put_object(struct memleak_object *object)
> > +{
> > + if (!atomic_dec_and_test(&object->use_count))
> > + return;
> > +
> > + /* should only get here after delete_object was called */
> > + BUG_ON(object->flags & OBJECT_ALLOCATED);
>
> This could be
>
> if (WARN_ON(object->flags & OBJECT_ALLOCATED))
> return;

I'm not sure just warning would be enough. If this happens, its a severe
bug in kmemleak and the tool is no longer useful (it could even leak
memory or free already freed blocks). I could change it to a
memleak_panic call but if the object use_count isn't reliable, the
memleak_disable call wouldn't work properly either.

> > +static void create_object(unsigned long ptr, size_t size, int min_count,
> > + gfp_t gfp)
> > +{
> > + unsigned long flags;
> > + struct memleak_object *object;
> > + struct prio_tree_node *node;
> > + struct stack_trace trace;
> > +
> > + object = kmem_cache_alloc(object_cache, gfp);
> > + if (!object)
> > + memleak_panic("kmemleak: Cannot allocate a memleak_object "
> > + "structure\n");
>
> Don't you want to exit early here if object == NULL?

Yes, indeed. That omission was caused by s/panic/memleak_panic/

> > + if (node != &object->tree_node) {
> > + unsigned long flags;
> > +
> > + pr_warning("kmemleak: Existing pointer\n");
> > + dump_stack();
>
> How come you don't dump_stack() or even WARN_ON() unconditionally in
> kmemleak_panic() which is called bit later so you can remove this kind
> of ad hoc logging?

Yes, I'll unify these via the memleak_panic() macro.

> > +static void delete_object(unsigned long ptr)
> > +{
> > + unsigned long flags;
> > + struct memleak_object *object;
> > +
> > + write_lock_irqsave(&memleak_lock, flags);
> > + object = lookup_object(ptr, 0);
> > + if (!object) {
> > + pr_warning("kmemleak: Freeing unknown object at 0x%08lx\n",
> > + ptr);
> > + dump_stack();
>
> Hmm, dump_stack() is called in quite a few places. Might make sense to
> add a memleak_report() function that does this in an uniform way.

Yes.

> > + write_unlock_irqrestore(&memleak_lock, flags);
> > + return;
> > + }
> > + prio_tree_remove(&object_tree_root, &object->tree_node);
> > + list_del_rcu(&object->object_list);
> > + write_unlock_irqrestore(&memleak_lock, flags);
> > +
> > + BUG_ON(!(object->flags & OBJECT_ALLOCATED));
> > + BUG_ON(atomic_read(&object->use_count) < 1);
>
> These could be converted to WARN_ON() calls, I think?

See my comment above, these are genuine kmemleak bugs and it shouldn't
just warn. Hopefully they will never happen unless a get/put_object is
missing.

Thanks.

--
Catalin



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