linux-kernel - Re: [PATCH] rcu: kasan: record and print kvfree_call

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Date:   Fri, 20 Nov 2020 06:45:50 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     "Zhang, Qiang" <qiang.zhang@...driver.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Uladzislau Rezki <urezki@...il.com>
Subject: Re: [PATCH] rcu: kasan: record and print kvfree_call_rcu call stack

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@...nel.org> wrote:
> > >
> > > On Wed, Nov 18, 2020 at 11:53:09AM +0800, qiang.zhang@...driver.com wrote:
> > > > From: Zqiang <qiang.zhang@...driver.com>
> > > >
> > > > Add kasan_record_aux_stack function for kvfree_call_rcu function to
> > > > record call stacks.
> > > >
> > > > Signed-off-by: Zqiang <qiang.zhang@...driver.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@...gle.com>