linux-kernel - Re: [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp

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Message-ID: <CAFULd4afgt7LtqzZ_oFDz4wtMe+TZKGX3E_XpSo2HD5rQEvOjg@mail.gmail.com>
Date: Wed, 20 Nov 2024 16:36:31 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Alex Elder <elder@...cstar.com>
Cc: linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chandan Babu R <chandan.babu@...cle.com>, "Darrick J. Wong" <djwong@...nel.org>, 
	Christoph Hellwig <hch@...radead.org>, Dave Chinner <dchinner@...hat.com>
Subject: Re: [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate()

On Wed, Nov 20, 2024 at 4:34 PM Alex Elder <elder@...cstar.com> wrote:
>
> On 11/20/24 9:06 AM, Uros Bizjak wrote:
> > try_cmpxchg() loop with constant "new" value can be substituted
> > with just xchg() to atomically get and clear the location.
>
> You're right.  With a constant new value (0), there is no need
> to loop to ensure we get a "stable" update.
>
> Is the READ_ONCE() is still needed?

No, xchg() guarantees atomic access on its own.

Uros.