linux-kernel - Re: fs/dlm/midcomms.c:913:22: sparse: sparse: restricted _

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Message-ID: <20220124220628.GL4285@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 24 Jan 2022 14:06:28 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Alexander Aring <aahringo@...hat.com>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        kernel test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, David Teigland <teigland@...hat.com>,
        cluster-devel <cluster-devel@...hat.com>,
        linux-sparse@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: fs/dlm/midcomms.c:913:22: sparse: sparse: restricted __le32
 degrades to integer

On Mon, Jan 24, 2022 at 04:36:55PM -0500, Alexander Aring wrote:
> Hi,
> 
> On Mon, Jan 24, 2022 at 3:23 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > On Mon, Jan 24, 2022 at 12:41:04PM -0500, Alexander Aring wrote:
> > > Hi,
> > >
> > > On Mon, Jan 24, 2022 at 12:36 PM Alexander Aring <aahringo@...hat.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > On Mon, Jan 24, 2022 at 12:21 PM Alexander Aring <aahringo@...hat.com> wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > On Mon, Jan 24, 2022 at 7:46 AM Dan Carpenter <dan.carpenter@...cle.com> wrote:
> > > > > >
> > > > > > On Sun, Jan 23, 2022 at 01:41:52PM -0500, Alexander Aring wrote:
> > > > > > >
> > > > > > > I see also:
> > > > > > >
> > > > > > > fs/dlm/midcomms.c:213:1: sparse: sparse: symbol
> > > > > > > '__srcu_struct_nodes_srcu' was not declared. Should it be static?
> > > > > > >
> > > > > >
> > > > > > Why not just do this?  (Untested.  Maybe I don't understand?)
> > > > > >
> > > > > > diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
> > > > > > index cb1f4351e8ba..a164089abec4 100644
> > > > > > --- a/include/linux/srcutree.h
> > > > > > +++ b/include/linux/srcutree.h
> > > > > > @@ -121,7 +121,7 @@ struct srcu_struct {
> > > > > >  #ifdef MODULE
> > > > > >  # define __DEFINE_SRCU(name, is_static)                                        \
> > > > > >         is_static struct srcu_struct name;                              \
> > > > > > -       struct srcu_struct * const __srcu_struct_##name                 \
> > > > > > +       is_static struct srcu_struct * const __srcu_struct_##name       \
> > > > > >                 __section("___srcu_struct_ptrs") = &name
> > > > > >  #else
> > > > > >  # define __DEFINE_SRCU(name, is_static)                                        \
> > > > > >
> > > > >
> > > > > I tried it and yes it will fix the issue and introduce another one
> > > > > about "is_static struct srcu_struct * const __srcu_struct_##name" is
> > > > > unused ("-Wunused-const-variable").
> > > > > I added a __maybe_unused after the introduced is_static and it seems
> > > > > to fix the introduced issue, now it compiles and sparse is happy. I am
> > > > > not sure if this is the right fix?
> > > >
> > > > it is obviously unused, but it has something to do with
> > > > "__section("___srcu_struct_ptrs")" and during module loading it, I
> > > > suppose, srcu tries to access it to find whatever needs to be
> > > > registered?
> > >
> > > Sorry, but if this is true then it can't be declared as static... and
> > > we are at the beginning again.
> >
> > Welcome to my world!!!  ;-)
> >
> > More seriously, thank you for chasing this down.  But would it work to
> > add a declaration just before?
> >
> 
> only if I add an "extern" in front of the declaration before, so it looks like:
> 
> extern struct srcu_struct * const __srcu_struct_##name;
> 
> (compile and sparse tested only)

If that works for everyone, it seems worth persuing.

One way to test this is as follows:

1.	Build a kernel with CONFIG_RCU_TORTURE_TEST=m.  Boot this and
	type "modprobe rcutorture torture_type=srcu".

	If you want to stop the torture test, type "rmmod rcutorture".

	This will test DEFINE_SRCU() for the module case.

2.	At the top-level directory of your Linux-kernel source tree,
	type "tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 3 --configs 'SRCU-N' --trust-make"

	This will test DEFINE_SRCU() for the non-module case.

If those both work, and if there are no other objections or complications,
please do send a patch.

							Thanx, Paul