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Message-ID: <1426381746.28068.70.camel@stgolabs.net>
Subject: Re: Question on mutex code
From: Davidlohr Bueso <dave@stgolabs.net>
To: Matthias Bonne <lemonlime51@gmail.com>
Cc: Yann Droneaud <ydroneaud@opteya.com>, kernelnewbies@kernelnewbies.org,
        linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>
Date: Sat, 14 Mar 2015 18:09:06 -0700
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On Sat, 2015-03-14 at 18:03 -0700, Davidlohr Bueso wrote:
> Good analysis, but not quite accurate for one simple fact: mutex
> trylocks _only_ use fastpaths (obviously just depend on the counter
> cmpxchg to 0), so you never fallback to the slowpath you are mentioning,
> thus the race is non existent. Please see the arch code.

For debug we use the trylock slowpath, but so does everything else, so
again you cannot hit this scenario.