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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Thu, 14 Jul 2016 09:41:58 +0100
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Subject: Re: [Qemu-devel] [RFC v2 11/11] tcg: Make tb_flush() thread safe
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To: Sergey Fedorov <sergey.fedorov@linaro.org>
Cc: qemu-devel@nongnu.org, MTTCG Devel <mttcg@listserver.greensocs.com>, KONRAD =?utf-8?B?RnLDqWTDqXJpYw==?= <fred.konrad@greensocs.com>, Alvise Rigo <a.rigo@virtualopensystems.com>, "Emilio G. Cota" <cota@braap.org>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>, Peter Maydell <peter.maydell@linaro.org>, Sergey Fedorov <serge.fdrv@gmail.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>


Sergey Fedorov <sergey.fedorov@linaro.org> writes:

> From: Sergey Fedorov <serge.fdrv@gmail.com>
>
> Use async_safe_run_on_cpu() to make tb_flush() thread safe.
>
> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
> ---
>
> Changes in v2:
>  - stale comment about unsafe tb_flush() removed
> ---
>  translate-all.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/translate-all.c b/translate-all.c
> index eaa95e4cd7dc..e69b5d4e889e 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -831,8 +831,7 @@ static void page_flush_tb(void)
>  }
>
>  /* flush all the translation blocks */
> -/* XXX: tb_flush is currently not thread safe */
> -void tb_flush(CPUState *cpu)
> +static void do_tb_flush(CPUState *cpu, void *data)
>  {
>  #if defined(DEBUG_FLUSH)
>      printf("qemu: flush code_size=%ld nb_tbs=%d avg_tb_size=%ld\n",
> @@ -861,6 +860,11 @@ void tb_flush(CPUState *cpu)
>      tcg_ctx.tb_ctx.tb_flush_count++;
>  }
>
> +void tb_flush(CPUState *cpu)
> +{
> +    async_safe_run_on_cpu(cpu, do_tb_flush, NULL);
> +}
> +
>  #ifdef DEBUG_TB_CHECK
>
>  static void
> @@ -1163,9 +1167,8 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>   buffer_overflow:
>          /* flush must be done */
>          tb_flush(cpu);
> -        /* cannot fail at this point */
> -        tb = tb_alloc(pc);
> -        assert(tb != NULL);
> +        mmap_unlock();
> +        cpu_loop_exit(cpu);

Given our other discussions about lock resetting I wonder if this is
another case where mmap_reset() could be called on cpu_loop_exit?

>      }
>
>      gen_code_buf = tcg_ctx.code_gen_ptr;

Otherwise so far the testing is looking pretty positive in linux-user:

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>


--
Alex Bennée