Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200721103016.3287832-1-elver@google.com> <20200721103016.3287832-5-elver@google.com>
 <20200721140929.GB10769@hirez.programming.kicks-ass.net>
In-Reply-To: <20200721140929.GB10769@hirez.programming.kicks-ass.net>
From:   Marco Elver <elver@google.com>
Date:   Tue, 21 Jul 2020 16:21:29 +0200
Message-ID: <CANpmjNNCrz+d6FOWCkC68NKO3PFToY1seRRKVQmn_KHa4D07hA@mail.gmail.com>
Subject: Re: [PATCH 4/8] kcsan: Add missing CONFIG_KCSAN_IGNORE_ATOMICS checks
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Mark Rutland <mark.rutland@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 21 Jul 2020 at 16:09, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Jul 21, 2020 at 12:30:12PM +0200, Marco Elver wrote:
> > Add missing CONFIG_KCSAN_IGNORE_ATOMICS checks for the builtin atomics
> > instrumentation.
> >
> > Signed-off-by: Marco Elver <elver@google.com>
> > ---
> > Added to this series, as it would otherwise cause patch conflicts.
> > ---
> >  kernel/kcsan/core.c | 25 +++++++++++++++++--------
> >  1 file changed, 17 insertions(+), 8 deletions(-)
> >
> > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> > index 4633baebf84e..f53524ea0292 100644
> > --- a/kernel/kcsan/core.c
> > +++ b/kernel/kcsan/core.c
> > @@ -892,14 +892,17 @@ EXPORT_SYMBOL(__tsan_init);
> >       u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder);                      \
> >       u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder)                       \
> >       {                                                                                          \
> > -             check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC);                      \
> > +             if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))                                      \
> > +                     check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC);              \
> >               return __atomic_load_n(ptr, memorder);                                             \
> >       }                                                                                          \
> >       EXPORT_SYMBOL(__tsan_atomic##bits##_load);                                                 \
> >       void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder);                   \
> >       void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder)                    \
> >       {                                                                                          \
> > -             check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC); \
> > +             if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))                                      \
> > +                     check_access(ptr, bits / BITS_PER_BYTE,                                    \
> > +                                  KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC);                    \
> >               __atomic_store_n(ptr, v, memorder);                                                \
> >       }                                                                                          \
> >       EXPORT_SYMBOL(__tsan_atomic##bits##_store)
> > @@ -908,8 +911,10 @@ EXPORT_SYMBOL(__tsan_init);
> >       u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder);                 \
> >       u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder)                  \
> >       {                                                                                          \
> > -             check_access(ptr, bits / BITS_PER_BYTE,                                            \
> > -                          KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC);    \
> > +             if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))                                      \
> > +                     check_access(ptr, bits / BITS_PER_BYTE,                                    \
> > +                                  KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
> > +                                          KCSAN_ACCESS_ATOMIC);                                 \
> >               return __atomic_##op##suffix(ptr, v, memorder);                                    \
> >       }                                                                                          \
> >       EXPORT_SYMBOL(__tsan_atomic##bits##_##op)
> > @@ -937,8 +942,10 @@ EXPORT_SYMBOL(__tsan_init);
> >       int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
> >                                                             u##bits val, int mo, int fail_mo)    \
> >       {                                                                                          \
> > -             check_access(ptr, bits / BITS_PER_BYTE,                                            \
> > -                          KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC);    \
> > +             if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))                                      \
> > +                     check_access(ptr, bits / BITS_PER_BYTE,                                    \
> > +                                  KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
> > +                                          KCSAN_ACCESS_ATOMIC);                                 \
> >               return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo);              \
> >       }                                                                                          \
> >       EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength)
> > @@ -949,8 +956,10 @@ EXPORT_SYMBOL(__tsan_init);
> >       u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
> >                                                          int mo, int fail_mo)                    \
> >       {                                                                                          \
> > -             check_access(ptr, bits / BITS_PER_BYTE,                                            \
> > -                          KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC);    \
> > +             if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))                                      \
> > +                     check_access(ptr, bits / BITS_PER_BYTE,                                    \
> > +                                  KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
> > +                                          KCSAN_ACCESS_ATOMIC);                                 \
> >               __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo);                       \
> >               return exp;                                                                        \
> >       }                                                                                          \
>
>
> *groan*, that could really do with a bucket of '{', '}'. Also, it is
> inconsistent in style with the existing use in
> DEFINE_TSAN_VOLATILE_READ_WRITE() where the define causes an early
> return.

Sadly we can't do an early return because we must always execute what
comes after the check. Unlike normal read/write instrumentation, TSAN
instrumentation for builtin atomics replaces the atomic with a call
into the runtime, and the runtime must also execute the atomic.

I'll add the {}.

Thanks,
-- Marco