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From:   Alexander Potapenko <glider@google.com>
Date:   Wed, 31 Aug 2022 09:13:20 +0200
Message-ID: <CAG_fn=Vwxmc6VwbJObiHNiPaAt9tAV77RqFco=q7traPG5DxYw@mail.gmail.com>
Subject: Re: [PATCH v5 04/44] x86: asm: instrument usercopy in get_user() and put_user()
To:     Yu Zhao <yuzhao@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Marco Elver <elver@google.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
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On Wed, Aug 31, 2022 at 1:07 AM Yu Zhao <yuzhao@google.com> wrote:
>
> On Tue, Aug 30, 2022 at 5:00 PM Andrew Morton <akpm@linux-foundation.org>=
 wrote:
> >
> > On Tue, 30 Aug 2022 16:25:24 -0600 Yu Zhao <yuzhao@google.com> wrote:
> >
> > > On Tue, Aug 30, 2022 at 4:05 PM Andrew Morton <akpm@linux-foundation.=
org> wrote:
> > > >
> > > > On Tue, 30 Aug 2022 16:23:44 +0200 Alexander Potapenko <glider@goog=
le.com> wrote:
> > > >
> > > > > >                  from init/do_mounts.c:2:
> > > > > > ./include/linux/page-flags.h: In function =E2=80=98page_fixed_f=
ake_head=E2=80=99:
> > > > > > ./include/linux/page-flags.h:226:36: error: invalid use of unde=
fined type =E2=80=98const struct page=E2=80=99
> > > > > >   226 |             test_bit(PG_head, &page->flags)) {
> > > > > >       |                                    ^~
> > > > > > ./include/linux/bitops.h:50:44: note: in definition of macro =
=E2=80=98bitop=E2=80=99
> > > > > >    50 |           __builtin_constant_p((uintptr_t)(addr) !=3D (=
uintptr_t)NULL) && \
> > > > > >       |                                            ^~~~
> > > > > > ./include/linux/page-flags.h:226:13: note: in expansion of macr=
o =E2=80=98test_bit=E2=80=99
> > > > > >   226 |             test_bit(PG_head, &page->flags)) {
> > > > > >       |             ^~~~~~~~
> > > > > > ...
> > > > >
> > > > > Gotcha, this is a circular dependency: mm_types.h -> sched.h ->
> > > > > kmsan.h -> gfp.h -> mmzone.h -> page-flags.h -> mm_types.h, where=
 the
> > > > > inclusion of sched.h into mm_types.h was only introduced in "mm:
> > > > > multi-gen LRU: support page table walks" - that's why the problem=
 was
> > > > > missing in other trees.
> > > >
> > > > Ah, thanks for digging that out.
> > > >
> > > > Yu, that inclusion is regrettable.
> > >
> > > Sorry for the trouble -- it's also superfluous because we don't call
> > > lru_gen_use_mm() when switching to the kernel.
> > >
> > > I've queued the following for now.
> >
> > Well, the rest of us want it too.
> >
> > > --- a/include/linux/mm_types.h
> > > +++ b/include/linux/mm_types.h
> > > @@ -3,7 +3,6 @@
> > >  #define _LINUX_MM_TYPES_H
> > >
> > >  #include <linux/mm_types_task.h>
> > > -#include <linux/sched.h>
> > >
> > >  #include <linux/auxvec.h>
> > >  #include <linux/kref.h>
> > > @@ -742,8 +741,7 @@ static inline void lru_gen_init_mm(struct mm_stru=
ct *mm)
> > >
> > >  static inline void lru_gen_use_mm(struct mm_struct *mm)
> > >  {
> > > -       if (!(current->flags & PF_KTHREAD))
> > > -               WRITE_ONCE(mm->lru_gen.bitmap, -1);
> > > +       WRITE_ONCE(mm->lru_gen.bitmap, -1);
> > >  }
> >
> > Doesn't apply.  I did:
> >
> > --- a/include/linux/mm_types.h~mm-multi-gen-lru-support-page-table-walk=
s-fix
> > +++ a/include/linux/mm_types.h
> > @@ -3,7 +3,6 @@
> >  #define _LINUX_MM_TYPES_H
> >
> >  #include <linux/mm_types_task.h>
> > -#include <linux/sched.h>
> >
> >  #include <linux/auxvec.h>
> >  #include <linux/kref.h>
> > @@ -742,11 +741,7 @@ static inline void lru_gen_init_mm(struc
> >
> >  static inline void lru_gen_use_mm(struct mm_struct *mm)
> >  {
> > -       /* unlikely but not a bug when racing with lru_gen_migrate_mm()=
 */
> > -       VM_WARN_ON_ONCE(list_empty(&mm->lru_gen.list));
>
> Yes. I got a report that somebody tripped over this "unlikely"
> condition (and ascertained it's not a bug). So I deleted this part as
> well.
>
> Will refresh the series around rc5. Thanks.

Guess I'd still proceed with splitting up kmsan.h just to be on the safe si=
de.

--=20
Alexander Potapenko
Software Engineer

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