linux-kernel - Re: [PATCH 3/4] locking/ww_mutex: Treat ww_mutex

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Date:   Wed, 17 Mar 2021 22:54:17 -0400
From:   Waiman Long <longman@...hat.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH 3/4] locking/ww_mutex: Treat ww_mutex_lock() like a
 trylock

On 3/17/21 10:24 PM, Boqun Feng wrote:
> Hi Waiman,
>
> Just a question out of curiosity: how does this problem hide so long?
> ;-) Because IIUC, both locktorture and ww_mutex_lock have been there for
> a while, so why didn't we spot this earlier?
>
> I ask just to make sure we don't introduce the problem because of some
> subtle problems in lock(dep).
>
You have to explicitly specify ww_mutex in the locktorture module 
parameter to run the test. ww_mutex is usually not the intended target 
of testing as there aren't that many places that use it. Even if someone 
run it, it probably is not on a debug kernel.

Our QA people try to run locktorture on ww_mutex and discover that.

Cheers,
Longman