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

[Marco Elver <elver@google.com>]

On Wed, 15 Jun 2022 at 23:17, Paul E. McKenney <paulmck@kernel.org> wrote:
>
> On Wed, Jun 15, 2022 at 01:40:39PM -0700, Paul E. McKenney wrote:
> > On Thu, Jun 16, 2022 at 04:26:16AM +0800, kernel test robot wrote:
> > > tree:   https://github.com/ammarfaizi2/linux-block paulmck/linux-rcu/pmladek.2022.06.15a
> > > head:   0ba7324b44282870af740a5a121add62c7f5f730
> > > commit: db21b02f8044e812f8a5e3811f602409290e3ede [133/140] context_tracking: Convert state to atomic_t
> > > config: x86_64-randconfig-r003-20220516 (https://download.01.org/0day-ci/archive/20220616/202206160411.v3iL3YC0-lkp@intel.com/config)
> > > compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
> > > reproduce (this is a W=1 build):
> > >         # https://github.com/ammarfaizi2/linux-block/commit/db21b02f8044e812f8a5e3811f602409290e3ede
> > >         git remote add ammarfaizi2-block https://github.com/ammarfaizi2/linux-block
> > >         git fetch --no-tags ammarfaizi2-block paulmck/linux-rcu/pmladek.2022.06.15a
> > >         git checkout db21b02f8044e812f8a5e3811f602409290e3ede
> > >         # save the config file
> > >         mkdir build_dir && cp config build_dir/.config
> > >         make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash
> > >
> > > If you fix the issue, kindly add following tag where applicable
> > > Reported-by: kernel test robot <lkp@intel.com>
> > >
> > > All warnings (new ones prefixed by >>):
> > >
> > > >> 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
> >
> > Marco, Dmitry, my guess is that this is due to the ct->active check in
> > both functions.  Are we supposed to do something to make this sort of
> > thing safe for KASAN?
>
> This time actually CCing Marco and Dmitry...

It's due to the atomic_read()s within the noinstr function. Within
noinstr you can use arch_atomic_read() to avoid the instrumentation.

Thanks,
-- Marco