linux-kernel - Re: [PATCH] tools/memory-model: document the "one-time init" pattern

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Message-ID: <CA+icZUVztkBRBhs_NQpTOg7rc34VkBQ1GCr5iXgw+P9XORwd9A@mail.gmail.com>
Date:   Fri, 17 Jul 2020 07:49:02 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        "Paul E . McKenney" <paulmck@...nel.org>,
        linux-fsdevel@...r.kernel.org, Akira Yokosawa <akiyks@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Dave Chinner <david@...morbit.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH] tools/memory-model: document the "one-time init" pattern

On Fri, Jul 17, 2020 at 6:48 AM Eric Biggers <ebiggers@...nel.org> wrote:
>
> From: Eric Biggers <ebiggers@...gle.com>
...
> This is motivated by the discussion at
> https://lkml.kernel.org/linux-fsdevel/20200713033330.205104-1-ebiggers@kernel.org/T/#u
...
> +In where cases where taking the mutex in the "already initialized" case

"In cases where..." (drop first "where")

> +presents scalability concerns, the implementation can be optimized to
> +check the 'inited' flag outside the mutex.  Unfortunately, this
> +optimization is often implemented incorrectly by using a plain load.
> +That violates the memory model and may result in unpredictable behavior.

- Sedat -