linux-kernel - Re: [PATCH] pstore/core: drop cmpxchg based updates

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Date:   Thu, 8 Sep 2016 12:23:56 +0200
From:   Rabin Vincent <rabin@....in>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>, groeck@...gle.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] pstore/core: drop cmpxchg based updates

On Wed, Aug 24, 2016 at 03:09:35PM +0200, Sebastian Andrzej Siewior wrote:
> I have here a FPGA behind PCIe which exports SRAM which I use for
> pstore. Now it seems that the FPGA no longer supports cmpxchg based
> updates and writes back 0xff…ff and returns the same.  This leads to
> crash during crash rendering pstore useless.
> Since I doubt that there is much benefit from using cmpxchg() here, I am
> dropping this atomic access and use the spinlock based version.
> 
> Cc: Anton Vorontsov <anton@...msg.org>
> Cc: Colin Cross <ccross@...roid.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Tony Luck <tony.luck@...el.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Tested-by: Rabin Vincent <rabinv@...s.com>

This patch is needed for pstore to work on (most?) ARMv7 chips.  See
this thread for details:
https://lkml.kernel.org/g/CABXOdTfT7xMfiBvRuUS1hsVs=q5q2wY1x1Z8oCyyJNFckM0g0A@mail.gmail.com