linux-kernel - Re: [PATCH 1/2] locktorture: doesn't check nreaders

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Date:   Fri, 18 Sep 2020 09:13:14 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     <paulmck@...nel.org>
CC:     Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        <linux-kernel@...r.kernel.org>, <rcu@...r.kernel.org>
Subject: Re: [PATCH 1/2] locktorture: doesn't check nreaders_stress when no
 readlock support

Hi Paul,

On 2020/9/18 0:58, Paul E. McKenney wrote:
> On Thu, Sep 17, 2020 at 09:59:09PM +0800, Hou Tao wrote:
>> To ensure there is always at least one locking thread.
>>
>> Signed-off-by: Hou Tao <houtao1@...wei.com>
>> ---
>>  kernel/locking/locktorture.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
>> index 9cfa5e89cff7f..bebdf98e6cd78 100644
>> --- a/kernel/locking/locktorture.c
>> +++ b/kernel/locking/locktorture.c
>> @@ -868,7 +868,8 @@ static int __init lock_torture_init(void)
>>  		goto unwind;
>>  	}
>>  
>> -	if (nwriters_stress == 0 && nreaders_stress == 0) {
>> +	if (nwriters_stress == 0 &&
>> +	    (!cxt.cur_ops->readlock || nreaders_stress == 0)) {
> 
> You lost me on this one.  How does it help to allow tests with zero
> writers on exclusive locks?  Or am I missing something subtle here?
> 
The purpose is to prohibit test with only readers on exclusive locks, not allow it.

So if the module parameters are "torture_type=mutex_lock nwriters_stress=0 nreaders_stress=3",
locktorture can fail early instead of continuing but doing nothing useful.

Regards,
Tao

> 							Thanx, Paul
> 
>>  		pr_alert("lock-torture: must run at least one locking thread\n");
>>  		firsterr = -EINVAL;
>>  		goto unwind;
>> -- 
>> 2.25.0.4.g0ad7144999
>>
> .
>