linux-kernel - Re: [RFC PATCH 5/8] sched: move CPU field back into thread_info if THREAD_INFO_IN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMj1kXH_Q4a4Gsi0Xuw=YsV-b7Mu8TQndk3Ei-JFaRV=GSiqUQ@mail.gmail.com>
Date:   Tue, 14 Sep 2021 17:52:59 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Keith Packard <keithpac@...zon.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: [RFC PATCH 5/8] sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y

On Tue, 14 Sept 2021 at 17:49, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Tue, Sep 14, 2021 at 5:11 AM Ard Biesheuvel <ardb@...nel.org> wrote:
> >
> >  static inline unsigned int task_cpu(const struct task_struct *p)
> >  {
> >  #ifdef CONFIG_THREAD_INFO_IN_TASK
> > -       return READ_ONCE(p->cpu);
> > +       return READ_ONCE(p->thread_info.cpu);
> >  #else
> >         return READ_ONCE(task_thread_info(p)->cpu);
> >  #endif
>
> Those two lines look different, but aren't.
>
> Please just remove the CONFIG_THREAD_INFO_IN_TASK conditional, and use
>
>           return READ_ONCE(task_thread_info(p)->cpu);
>
> unconditionally, which now does the right thing regardless.
>

Unfortunately not.

task_cpu() takes a 'const struct task_struct *', whereas
task_thread_info() takes a 'struct task_struct *'.

Since task_thread_info()-><foo> is widely used as an lvalue, I would
need to update task_cpu()'s prototype and fix up all the callers, some
of which take the const flavor themselves. Or introduce
'const_task_thread_info()' which takes the const flavor, and cannot be
used to instantiate lvalues.

Suggestions welcome, but this is the cleanest I could come up with.