linux-kernel - Re: [PATCH v2] buffer: Fix I/O error due to ARM read-after-read hazard

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Message-ID: <20191121165334.GB4905@willie-the-truck>
Date:   Thu, 21 Nov 2019 16:53:35 +0000
From:   Will Deacon <will@...nel.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     linux@...linux.org.uk, torvalds@...ux-foundation.org,
        catalin.marinas@....com, vincent.whitchurch@...s.com,
        axboe@...nel.dk, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, rabinv@...s.com,
        Richard.Earnshaw@....com
Subject: Re: [PATCH v2] buffer: Fix I/O error due to ARM read-after-read
 hazard

On Thu, Nov 21, 2019 at 09:25:33AM +0800, Herbert Xu wrote:
> On Wed, Nov 20, 2019 at 07:18:40PM +0000, Will Deacon wrote:
> >
> > > The Alpha barrier matters for pointers, how could it make a
> > > difference for individual bits?
> > 
> > I guess you could use the result of test_bit to index into an array or
> > something?
> 
> Can Alpha Assembly even do this without using a branch?

Don't see why not: you can add the base address to the scaled result
of test_bit and use that as the address register into a load instruction.

Will