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Subject: Re: [PATCH 3/4] locking/ww_mutex: Treat ww_mutex_lock() like a
 trylock
To:     Boqun Feng <boqun.feng@gmail.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        linux-kernel@vger.kernel.org, Juri Lelli <juri.lelli@redhat.com>
References: <20210316153119.13802-1-longman@redhat.com>
 <20210316153119.13802-4-longman@redhat.com>
 <YFK5yBIOTiCdFLNm@boqun-archlinux>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <64af1d7b-6720-0ac1-4a55-bb0acb642c6f@redhat.com>
Date:   Wed, 17 Mar 2021 22:54:17 -0400
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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