linux-kernel - Re: [PATCH 3/4] locking/rwbase: Fix rwbase_write_lock() vs __rwbase_read

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Message-ID: <87sfy7b3rr.ffs@tglx>
Date:   Tue, 14 Sep 2021 17:00:56 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     boqun.feng@...il.com, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mike Galbraith <efault@....de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH 3/4] locking/rwbase: Fix rwbase_write_lock() vs
 __rwbase_read_lock()

On Tue, Sep 14 2021 at 15:59, Peter Zijlstra wrote:
> On Tue, Sep 14, 2021 at 09:45:12AM +0200, Thomas Gleixner wrote:
>> The read/set is always in the same lock instance.
>
> I really did make a mess of things didn't I :-/ It was some intermediate
> state that was broken.

Thinking about memory ordering can reorder your memory :)

> How's this then?
>
> ---
> Subject: locking/rwbase: Extract __rwbase_write_trylock()
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Thu, 09 Sep 2021 12:59:18 +0200
>
> The code in rwbase_write_lock() is a little non-obvious vs the
> read+set 'trylock', extract the sequence into a helper function to
> clarify the code.
>
> This also provides a single site to fix fast-path ordering.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>