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

[Thomas Gleixner]

On Tue, Aug 03 2021 at 13:20, Peter Zijlstra wrote:
> On Fri, Jul 30, 2021 at 03:51:05PM +0200, Thomas Gleixner wrote:
>> +	/*
>> +	 * We were woken prior to requeue by a timeout or a signal.
>> +	 * Unqueue the futex_q and determine which it was.
>> +	 */
>> +	plist_del(&q->list, &hb->chain);
>> +	hb_waiters_dec(hb);
>> +
>> +	/* Handle spurious wakeups gracefully */
>> +	ret = -EWOULDBLOCK;
>> +	if (timeout && !timeout->task)
>> +		ret = -ETIMEDOUT;
>> +	else if (signal_pending(current))
>> +		ret = -ERESTARTNOINTR;
>>  	return ret;
>>  }
>
> AFAICT this change is a separate cleanup, possible because the only
> callsite already does that match_futex() test before calling this.

No. It's possible because the state machine guarantees that. The
match_futex() in the calling function is unrelated.

> I think it might be worth splitting out, just to reduce the complexity
> of this patch.

Yes, I did by moving the match_futex() test to the call site as a
preparatory change for this one.

Thanks,

        tglx