linux-kernel - Re: [PATCH] Fix data race in mark_rt_mutex

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Message-ID: <Y87FLV0dWSyQz3NZ@rowland.harvard.edu>
Date:   Mon, 23 Jan 2023 12:34:37 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Hernan Ponce de Leon <hernan.poncedeleon@...weicloud.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        peterz@...radead.org, mingo@...hat.com, will@...nel.org,
        longman@...hat.com, boqun.feng@...il.com, akpm@...l.org,
        tglx@...utronix.de, joel@...lfernandes.org,
        diogo.behrens@...wei.com, jonas.oberhauser@...wei.com,
        linux-kernel@...r.kernel.org,
        Hernan Ponce de Leon <hernanl.leon@...wei.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] Fix data race in mark_rt_mutex_waiters

On Mon, Jan 23, 2023 at 08:40:14AM -0800, Paul E. McKenney wrote:
> In the case, the value read is passed into cmpxchg_relaxed(), which
> checks the value against memory.  In this case, as Arjan noted, the only
> compiler-and-silicon difference between data_race() and READ_ONCE()
> is that use of data_race() might allow the compiler to do things like
> tear the load, thus forcing the occasional spurious cmpxchg_relaxed()
> failure.

Is it possible in theory for a torn load to cause a spurious 
cmpxchg_relaxed() success?  Or would that not matter here?

Alan