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From: "Paul E. McKenney" <[email protected]>
To: Marco Elver <[email protected]>
Cc: kernel test robot <[email protected]>,
	Frederic Weisbecker <[email protected]>,
	[email protected],
	GNU/Weeb Mailing List <[email protected]>,
	[email protected], [email protected]
Subject: Re: [ammarfaizi2-block:paulmck/linux-rcu/pmladek.2022.06.15a 133/140] vmlinux.o: warning: objtool: __ct_user_exit+0x41: call to __kasan_check_read() leaves .noinstr.text section
Date: Thu, 16 Jun 2022 10:49:38 -0700	[thread overview]
Message-ID: <20220616174938.GR1790663@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <CANpmjNPhfGnO8qebvPd2pEqO37qTAa8pUAOTy2MXqT4R+iZ8QA@mail.gmail.com>

On Thu, Jun 16, 2022 at 07:32:14PM +0200, Marco Elver wrote:
> On Thu, 16 Jun 2022 at 18:44, Paul E. McKenney <[email protected]> wrote:
> [...]
> > > > > > > >> vmlinux.o: warning: objtool: __ct_user_exit+0x41: call to __kasan_check_read() leaves .noinstr.text section
> > > > > > > >> vmlinux.o: warning: objtool: __ct_user_enter+0x7f: call to __kasan_check_read() leaves .noinstr.text section
> [...]
> > > > It's due to the atomic_read()s within the noinstr function. Within
> > > > noinstr you can use arch_atomic_read() to avoid the instrumentation.
> > >
> > > Thank you, will fix!
> >
> > And please see below for an alleged fix.
> 
> Looks good, if this made the above warnings go away.

Here is hoping!  I will see if I can reproduce locally.  ;-)

> Btw, it's not just KASAN, but arch_atomic_read() also disables KCSAN
> checking. A similar warning would have been generated in a KCSAN
> config.

Good to know, thank you!  Additional local-reproduce opportunities.

> Reviewed-by: Marco Elver <[email protected]>

Applied, thank you!

                                                         Thanx, Paul

> > ------------------------------------------------------------------------
> >
> > commit 81e24ca26ee9933bcacf67a61e3f6ae41a025442
> > Author: Paul E. McKenney <[email protected]>
> > Date:   Thu Jun 16 09:30:37 2022 -0700
> >
> >     context_tracking: Use arch_atomic_read() in __ct_state for KASAN
> >
> >     Context tracking's __ct_state() function can be invoked from noinstr state
> >     where RCU is not watching.  This means that its use of atomic_read()
> >     causes KASAN to invoke the non-noinstr __kasan_check_read() function
> >     from the noinstr function __ct_state().  This is problematic because
> >     someone tracing the __kasan_check_read() function could get a nasty
> >     surprise because of RCU not watching.
> >
> >     This commit therefore replaces the __ct_state() function's use of
> >     atomic_read() with arch_atomic_read(), which KASAN does not attempt to
> >     add instrumention to.
> >
> >     Signed-off-by: Paul E. McKenney <[email protected]>
> >     Cc: Frederic Weisbecker <[email protected]>
> >     Cc: Marco Elver <[email protected]>
> >
> > diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
> > index 0aecc07fb4f50..81c51e5f03143 100644
> > --- a/include/linux/context_tracking_state.h
> > +++ b/include/linux/context_tracking_state.h
> > @@ -49,7 +49,7 @@ DECLARE_PER_CPU(struct context_tracking, context_tracking);
> >
> >  static __always_inline int __ct_state(void)
> >  {
> > -       return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
> > +       return arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
> >  }
> >  #endif
> >

      reply	other threads:[~2022-06-16 17:49 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-15 20:26 [ammarfaizi2-block:paulmck/linux-rcu/pmladek.2022.06.15a 133/140] vmlinux.o: warning: objtool: __ct_user_exit+0x41: call to __kasan_check_read() leaves .noinstr.text section kernel test robot
2022-06-15 20:40 ` Paul E. McKenney
2022-06-15 21:17   ` Paul E. McKenney
2022-06-16  8:19     ` Marco Elver
2022-06-16 13:40       ` Paul E. McKenney
2022-06-16 16:44         ` Paul E. McKenney
2022-06-16 17:32           ` Marco Elver
2022-06-16 17:49             ` Paul E. McKenney [this message]

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