linux-kernel - Re: [RFC PATCH 3/3] pstore/ram: avoid atomic accesses for ioremapped regions

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Date:	Wed, 10 Apr 2013 10:55:35 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Colin Cross <ccross@...roid.com>
CC:	lkml <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Anton Vorontsov <cbouatmailru@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [RFC PATCH 3/3] pstore/ram: avoid atomic accesses for ioremapped
 regions

On 04/09/2013 11:10 PM, Colin Cross wrote:
> On Tue, Apr 9, 2013 at 8:08 PM, Rob Herring <robherring2@...il.com> wrote:
>> From: Rob Herring <rob.herring@...xeda.com>
>>
>> For persistent RAM outside of main memory, the memory may have limitations
>> on supported accesses. For internal RAM on highbank platform exclusive
>> accesses are not supported and will hang the system. So atomic_cmpxchg
>> cannot be used. This commit uses spinlock protection for buffer size and
>> start updates on ioremapped regions instead.
> 
> I used atomics in persistent_ram to support persistent ftrace, which
> now exists as PSTORE_FTRACE.  At some point during development I had
> trouble with recursive tracing causing an infinite loop, so you may
> want to test that calling out to spinlock functions with PSTORE_FTRACE
> turned on and enabled doesn't cause a problem.

I've tested that now and it appears to work fine. Was there some
specific setup of ftrace that caused problems?

Rob

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