Re: [Qemu-devel] [RFC 8/8] tcg: Make tb_flush() thread safe

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 28/06/16 19:18, Alex Bennée wrote:
> 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>
>> ---
>>  translate-all.c | 12 ++++++++----
>>  1 file changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/translate-all.c b/translate-all.c
>> index 3f402dfe04f5..09b1d0b0efc3 100644
>> --- a/translate-all.c
>> +++ b/translate-all.c
>> @@ -832,7 +832,7 @@ static void page_flush_tb(void)
>>
>>  /* flush all the translation blocks */
>>  /* XXX: tb_flush is currently not thread safe */
>            ^^^
>
> The comment belies a lack of confidence ;-)

Nice catch!

Thanks,
Sergey

>
>> -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 +861,11 @@ 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 +1168,8 @@ 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);
>>      }
>>
>>      gen_code_buf = tcg_ctx.code_gen_ptr;
>
> --
> Alex Bennée