Re: [PATCH] rcu: kasan: record and print kvfree_call_rcu call stack

Paul E. McKenney
2020-11-20T14:46:13Z

On Fri, Nov 20, 2020 at 06:34:40AM -0800, Paul E. McKenney wrote:
> On Fri, Nov 20, 2020 at 09:51:15AM +0100, Dmitry Vyukov wrote:
> > On Thu, Nov 19, 2020 at 10:49 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> > >
> > > On Wed, Nov 18, 2020 at 11:53:09AM +0800, qiang.zhang@windriver.com wrote:
> > > > From: Zqiang <qiang.zhang@windriver.com>
> > > >
> > > > Add kasan_record_aux_stack function for kvfree_call_rcu function to
> > > > record call stacks.
> > > >
> > > > Signed-off-by: Zqiang <qiang.zhang@windriver.com>
> > >
> > > Thank you, but this does not apply on the "dev" branch of the -rcu tree.
> > > See file:///home/git/kernel.org/rcutodo.html for more info.
> > >
> > > Adding others on CC who might have feedback on the general approach.
> > >
> > > Thanx, Paul
> > >
> > > > ---
> > > > kernel/rcu/tree.c | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > > index da3414522285..a252b2f0208d 100644
> > > > --- a/kernel/rcu/tree.c
> > > > +++ b/kernel/rcu/tree.c
> > > > @@ -3506,7 +3506,7 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> > > > success = true;
> > > > goto unlock_return;
> > > > }
> > > > -
> > > > + kasan_record_aux_stack(ptr);
> > > > success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr);
> > > > if (!success) {
> > > > run_page_cache_worker(krcp);
> >
> > kvfree_call_rcu is intended to free objects, right? If so this is:
>
> True, but mightn't there still be RCU readers referencing this object for
> some time, as in up to the point that the RCU grace period ends? If so,
> won't adding this cause KASAN to incorrectly complain about those readers?
>
> Or am I missing something here?

For example, is kasan_record_aux_stack() -only- recording the stack and
not at all updating the allocated/freed state?

Thanx, Paul

> > Acked-by: Dmitry Vyukov <dvyukov@google.com>