Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 17 Oct 2019 09:47:30 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Marco Elver <elver@google.com>
Cc:     LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Alexander Potapenko <glider@google.com>,
        Andrea Parri <parri.andrea@gmail.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Boqun Feng <boqun.feng@gmail.com>,
        Borislav Petkov <bp@alien8.de>, Daniel Axtens <dja@axtens.net>,
        Daniel Lustig <dlustig@nvidia.com>,
        dave.hansen@linux.intel.com, David Howells <dhowells@redhat.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Joel Fernandes <joel@joelfernandes.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Luc Maranget <luc.maranget@inria.fr>,
        Mark Rutland <mark.rutland@arm.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        linux-arch <linux-arch@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        linux-efi@vger.kernel.org,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [PATCH 1/8] kcsan: Add Kernel Concurrency Sanitizer
 infrastructure
Message-ID: <20191017074730.GW2328@hirez.programming.kicks-ass.net>
References: <20191016083959.186860-1-elver@google.com>
 <20191016083959.186860-2-elver@google.com>
 <20191016184346.GT2328@hirez.programming.kicks-ass.net>
 <CANpmjNP4b9Eo3ZKE6maBs4ANS7K7sLiVB2CbebQnCH09TB+hZQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CANpmjNP4b9Eo3ZKE6maBs4ANS7K7sLiVB2CbebQnCH09TB+hZQ@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Oct 16, 2019 at 09:34:05PM +0200, Marco Elver wrote:
> On Wed, 16 Oct 2019 at 20:44, Peter Zijlstra <peterz@infradead.org> wrote:
> > > +     /*
> > > +      * Disable interrupts & preemptions, to ignore races due to accesses in
> > > +      * threads running on the same CPU.
> > > +      */
> > > +     local_irq_save(irq_flags);
> > > +     preempt_disable();
> >
> > Is there a point to that preempt_disable() here?
> 
> We want to avoid being preempted while the watchpoint is set up;
> otherwise, we would report data-races for CPU-local data, which is
> incorrect.

Disabling IRQs already very much disables preemption. There is
absolutely no point in doing preempt_disable() when the whole section
already runs with IRQs disabled.