linux-kernel - Re: [PATCH 0/2] ARM: omap2+: omap_hwmod: Fix false lockdep warning

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Date:	Fri, 6 Feb 2015 21:26:07 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Tony Lindgren <tony@...mide.com>, <paul@...an.com>,
	<linux-omap@...r.kernel.org>, <mingo@...hat.com>,
	<linux-kernel@...r.kernel.org>, <balbi@...com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 0/2] ARM: omap2+: omap_hwmod: Fix false lockdep warning

On 02/06/2015 08:32 PM, Peter Zijlstra wrote:
> On Fri, Feb 06, 2015 at 06:05:32PM +0200, Peter Ujfalusi wrote:
>> Certainly looks much simpler, but it adds quite a bit of data to the
>> omap_hwmod struct, and we have a _lot_ of them for omap2plus configuration.
>>
>> ls -al vmlinux
>>
>> w/o any the lockdep warning fixes:
>> 110109168
>>
>> With my series applied:
>> 110112031 (base + 2863)
>>
>> With setting individual lockdep class:
>> 110114275 (base + 5107)
>>
>> I certainly like the lockdep_set_class() way since it is cleaner, but it adds
>> almost double amount of bytes to the kernel.
> 
> Yeah, I've never really bothered with data too much, its a debug
> feature. So lock_class_key is 8 bytes, and strictly speaking you could
> union them over other fields, all we really need is unique addresses, we
> don't actually use the storage.

True. our omap2plus defconfig does not have LOCKDEP enabled so it should not
add anything to the data when running default kernel.
I'll test the lockdep_set_class() method you suggested on Monday (not
tomorrow), but still as first thing.
If it is working as expected I'll send a patch with you as author.

Thanks,
Péter
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