Re: [patch 58/63] futex: Prevent requeue_pi() lock nesting issue on RT

[Thomas Gleixner]

On Tue, Aug 03 2021 at 12:07, Peter Zijlstra wrote:

> On Fri, Jul 30, 2021 at 03:51:05PM +0200, Thomas Gleixner wrote:
>> @@ -219,6 +221,10 @@ struct futex_q {
>>  	struct rt_mutex_waiter *rt_waiter;
>>  	union futex_key *requeue_pi_key;
>>  	u32 bitset;
>> +	atomic_t requeue_state;
>> +#ifdef CONFIG_PREEMPT_RT
>> +	struct rcuwait requeue_wait;
>> +#endif
>>  } __randomize_layout;
>>  
>>  static const struct futex_q futex_q_init = {
>
> Do we want to explicitly initialize requeue_state in futex_q_init? I was
> looking where we reset the state machine and eventually figured it out,
> but I'm thinking something more explicit might help avoid this for the
> next time.

Sure.