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

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Date:	Mon, 9 Feb 2015 10:27:32 +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>,
	Tero Kristo <t-kristo@...com>
Subject: Re: [PATCH 0/2] ARM: omap2+: omap_hwmod: Fix false lockdep warning

On 02/06/2015 09:26 PM, Peter Ujfalusi wrote:
>> 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.

With omap2plus_defconfig my build produces (vmlinux size):
Base: 				99905522
with my series:			99908385 (base + 2863)
with Peter Zijlstra's patch:	99910625 (base + 5103)

The reason for this is that we will only have
struct lock_class_key { };
in case of !CONFIG_LOCKDEP. On ARM however CONFIG_LOCKDEP is enabled by
default, while the CONFIG_DEBUG_LOCKDEP is disabled.

So it does add more data to our default omap2plus config.

Tony: do you have preference on the way we fix this issue?

As I recall there is a plan to remove the hwmod static database and move it or
generate it from DT? Not sure when and how this will be done, but will it
affect the lockdep_set_class() way?

-- 
Péter
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