linux-kernel - Re: [PATCH] staging: zcache: fix serialization bug in zv stats

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Message-ID: <4EFDF671.7020101@linux.vnet.ibm.com>
Date:	Fri, 30 Dec 2011 11:35:45 -0600
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	Greg Kroah-Hartman <gregkh@...e.de>,
	Brian King <brking@...ux.vnet.ibm.com>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	Konrad Wilk <konrad.wilk@...cle.com>,
	Nitin Gupta <ngupta@...are.org>
Subject: Re: [PATCH] staging: zcache: fix serialization bug in zv stats

On 12/30/2011 11:02 AM, Dan Magenheimer wrote:
>> From: Seth Jennings [mailto:sjenning@...ux.vnet.ibm.com]
>> Sent: Friday, December 30, 2011 9:42 AM
>> To: Greg Kroah-Hartman
>> Cc: Seth Jennings; Dan Magenheimer; Brian King; devel@...verdev.osuosl.org; linux-
>> kernel@...r.kernel.org
>> Subject: [PATCH] staging: zcache: fix serialization bug in zv stats
>>
>> In a multithreaded workload, the zv_curr_dist_counts
>> and zv_cumul_dist_counts statistics are being corrupted
>> because the increments and decrements in zv_create
>> and zv_free are not atomic.
>>
>> This patch converts these statistics and their corresponding
>> increments/decrements/reads to atomic operations.
>>
>> Based on v3.2-rc7
>>
>> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> 
> I'm inclined to nack this change, at least unless inside an #ifdef DEBUG,

I guess I didn't respond to this suggestion.  We could put #ifdef DEBUG
around the updates in zv_create and zv_free and around the two sysfs
*_show functions.  Kinda messy though.  I guess it might not matter
if we'll be re-evaluating this whole thing soon.

I'd just like to have it correct in mainline until then.

--
Seth

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