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From:   Marco Elver <elver@google.com>
Date:   Tue, 30 May 2023 09:40:31 +0200
Message-ID: <CANpmjNN1VWdwEVouVfPHZqYYszPNo=TbmXt6na9q+DuOkXY3xA@mail.gmail.com>
Subject: Re: [PATCH] powerpc/kcsan: Properly instrument arch_spin_unlock()
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
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On Mon, 29 May 2023 at 17:50, Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
> The following boottime error is encountered with SMP kernel:
>
>   kcsan: improperly instrumented type=(0): arch_spin_unlock(&arch_spinlock)
>   kcsan: improperly instrumented type=(0): spin_unlock(&test_spinlock)
>   kcsan: improperly instrumented type=(KCSAN_ACCESS_WRITE): arch_spin_unlock(&arch_spinlock)
>   kcsan: improperly instrumented type=(KCSAN_ACCESS_WRITE): spin_unlock(&test_spinlock)
>   kcsan: improperly instrumented type=(KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND): arch_spin_unlock(&arch_spinlock)
>   kcsan: improperly instrumented type=(KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND): spin_unlock(&test_spinlock)
>   kcsan: selftest: test_barrier failed
>   kcsan: selftest: 2/3 tests passed
>   Kernel panic - not syncing: selftests failed
>
> Properly instrument arch_spin_unlock() with kcsan_mb().
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>

Acked-by: Marco Elver <elver@google.com>

> ---
>  arch/powerpc/include/asm/simple_spinlock.h | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/simple_spinlock.h b/arch/powerpc/include/asm/simple_spinlock.h
> index 9dcc7e9993b9..4dd12dcb9ef8 100644
> --- a/arch/powerpc/include/asm/simple_spinlock.h
> +++ b/arch/powerpc/include/asm/simple_spinlock.h
> @@ -15,6 +15,7 @@
>   * (the type definitions are in asm/simple_spinlock_types.h)
>   */
>  #include <linux/irqflags.h>
> +#include <linux/kcsan-checks.h>
>  #include <asm/paravirt.h>
>  #include <asm/paca.h>
>  #include <asm/synch.h>
> @@ -126,6 +127,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
>
>  static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  {
> +       kcsan_mb();
>         __asm__ __volatile__("# arch_spin_unlock\n\t"
>                                 PPC_RELEASE_BARRIER: : :"memory");
>         lock->slock = 0;
> --
> 2.40.1
>