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Date:   Fri, 18 Sep 2020 10:59:11 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Hou Tao <houtao1@huawei.com>
Cc:     Josh Triplett <josh@joshtriplett.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        linux-kernel@vger.kernel.org, rcu@vger.kernel.org
Subject: Re: [PATCH v2 1/2] locktorture: doesn't check nreaders_stress when
 no readlock support
Message-ID: <20200918175911.GV29330@paulmck-ThinkPad-P72>
Reply-To: paulmck@kernel.org
References: <20200918033755.GS29330@paulmck-ThinkPad-P72>
 <20200918114424.100852-1-houtao1@huawei.com>
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On Fri, Sep 18, 2020 at 07:44:24PM +0800, Hou Tao wrote:
> When do locktorture for exclusive lock which doesn't have readlock
> support, the following module parameters will be considered as valid:
> 
>  torture_type=mutex_lock nwriters_stress=0 nreaders_stress=1
> 
> But locktorture will do nothing useful, so instead of permitting
> these useless parameters, let's reject these parameters by returning
> -EINVAL during module init.
> 
> Signed-off-by: Hou Tao <houtao1@huawei.com>

Much better, much easier for people a year from now to understand.
Queued for v5.11, thank you!

I did edit the commit log a bit as shown below, so please let me
know if I messed anything up.

							Thanx, Paul

commit 4985c52e3b5237666265e59f56856f485ee36e71
Author: Hou Tao <houtao1@huawei.com>
Date:   Fri Sep 18 19:44:24 2020 +0800

    locktorture: Ignore nreaders_stress if no readlock support
    
    Exclusive locks do not have readlock support, which means that a
    locktorture run with the following module parameters will do nothing:
    
     torture_type=mutex_lock nwriters_stress=0 nreaders_stress=1
    
    This commit therefore rejects this combination for exclusive locks by
    returning -EINVAL during module init.
    
    Signed-off-by: Hou Tao <houtao1@huawei.com>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 316531d..046ea2d 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -870,7 +870,8 @@ 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)) {
 		pr_alert("lock-torture: must run at least one locking thread\n");
 		firsterr = -EINVAL;
 		goto unwind;