linux-kernel - Re: [PATCH] MIPS: c-r4k: fix data corruption related to cache coherence.

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Message-ID: <20180425220834.GC25917@saruman>
Date:   Wed, 25 Apr 2018 23:08:34 +0100
From:   James Hogan <jhogan@...nel.org>
To:     NeilBrown <neil@...wn.name>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>, linux-mips@...ux-mips.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: c-r4k: fix data corruption related to cache
 coherence.

On Thu, Apr 26, 2018 at 08:00:18AM +1000, NeilBrown wrote:
> On Wed, Apr 25 2018, James Hogan wrote:
> > So I'm thinking "!mips_cm_present()" should probably be replaced with
> > "!r4k_op_needs_ipi(R4K_INDEX)" (and the comment updated to mention that
> > IPI calls aren't implemented here).
> 
> That makes sense.  I tried ipi calls at one stage.  Synchronous ones
> cannot be used because this code is called with interrupts disabled, and
> async ones cannot provide the required guarantees.

Okay. I thought something like that might be the case.

> 
> I'll update the patch, test that it still works, and resend, in the next
> day or so.

Thanks. It wouldn't hurt to also mention why IPIs can't be used in the
code comments, if its fresh in your mind, just for the benefit of next
person to attempt it.

Cheers
James

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