Re: [Qemu-devel] [PATCH 03/10] replace spinlock by QemuMutex.

[Paolo Bonzini]

On 13/08/2015 14:17, Frederic Konrad wrote:
>> diff --git a/linux-user/main.c b/linux-user/main.c
>> index fdee981..fd06ce9 100644
>> --- a/linux-user/main.c
>> +++ b/linux-user/main.c
>> @@ -107,7 +107,7 @@ static int pending_cpus;
>>   /* Make sure everything is in a consistent state for calling
>> fork().  */
>>   void fork_start(void)
>>   {
>> -    pthread_mutex_lock(&tcg_ctx.tb_ctx.tb_lock);
>> +    qemu_mutex_lock(&tcg_ctx.tb_ctx.tb_lock);
>>       pthread_mutex_lock(&exclusive_lock);
>>       mmap_fork_start();
>>   }
>> @@ -129,11 +129,11 @@ void fork_end(int child)
>>           pthread_mutex_init(&cpu_list_mutex, NULL);
>>           pthread_cond_init(&exclusive_cond, NULL);
>>           pthread_cond_init(&exclusive_resume, NULL);
>> -        pthread_mutex_init(&tcg_ctx.tb_ctx.tb_lock, NULL);
>> +        qemu_mutex_init(&tcg_ctx.tb_ctx.tb_lock);
>>           gdbserver_fork(thread_cpu);
>>       } else {
>>           pthread_mutex_unlock(&exclusive_lock);
>> -        pthread_mutex_unlock(&tcg_ctx.tb_ctx.tb_lock);
>> +        qemu_mutex_unlock(&tcg_ctx.tb_ctx.tb_lock);
> We might want to use tb_lock/unlock in user code as well instead of
> calling directly qemu_mutex_* ?

You cannot do that because of the recursive locking assertions; the
child is not using qemu_mutex_unlock, it's using qemu_mutex_init.  So I
would have to add some kind of tb_lock_reset_after_fork() function which
is a bit ugly.

>> @@ -676,6 +709,7 @@ static inline void code_gen_alloc(size_t tb_size)
>>               CODE_GEN_AVG_BLOCK_SIZE;
>>       tcg_ctx.tb_ctx.tbs =
>>               g_malloc(tcg_ctx.code_gen_max_blocks *
>> sizeof(TranslationBlock));
>> +    qemu_mutex_init(&tcg_ctx.tb_ctx.tb_lock);
> Maybe we can initialize the mutex only for CONFIG_USER_ONLY?

It's okay, it doesn't consume system resources.

Paolo