linux-kernel - Re: [PATCH v3 2/2] MIPS: io: add a barrier after register read in readX()

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Message-ID: <20180412215855.GB27802@saruman>
Date:   Thu, 12 Apr 2018 22:58:55 +0100
From:   James Hogan <jhogan@...nel.org>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     linux-mips@...ux-mips.org, arnd@...db.de, timur@...eaurora.org,
        sulrich@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] MIPS: io: add a barrier after register read in
 readX()

On Thu, Apr 12, 2018 at 10:51:49PM +0100, James Hogan wrote:
> On Tue, Apr 03, 2018 at 08:55:04AM -0400, Sinan Kaya wrote:
> > While a barrier is present in writeX() function before the register write,
> > a similar barrier is missing in the readX() function after the register
> > read. This could allow memory accesses following readX() to observe
> > stale data.
> > 
> > Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> > Reported-by: Arnd Bergmann <arnd@...db.de>
> 
> Both patches look like obvious improvements to me, so I'm happy to apply
> to my fixes branch.

Though having said that, a comment to go with the rmb() (as suggested by
checkpatch) to detail the situation we're concerned about would be nice
to have.

Cheers
James

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