linux-kernel - Re: [PATCH 1/2] Staging: zram: Turn lockdep off during zram_init

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Message-ID: <20111203173834.GM9190@smp.if.uj.edu.pl>
Date:	Sat, 3 Dec 2011 18:38:35 +0100
From:	Witold Baryluk <baryluk@....if.uj.edu.pl>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jerome Marchand <jmarchan@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Nitin Gupta <ngupta@...are.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] Staging: zram: Turn lockdep off during
 zram_init_device()

On 11-30 14:59, Peter Zijlstra wrote:
> On Wed, 2011-11-30 at 14:14 +0100, Jerome Marchand wrote:
> > zram->init_lock can be hold over an allocation that may try to reclaim
> > memory in zram_init_device(). The same lock can later be taken from a
> > reclaim context in zram_make_request(), thus triggering a lockdep
> > warning. However, memory can not be reclaimed to an uninitialized zram
> > device. Therefore, this warning is a false positive.
> > To prevent the warning to occur, we turn lockdep off during while the
> > device is initialized.
> 
> fuck no! why do you even remotely consider this a sane thing to do?
> 
> There's tons of lockdep annotations, try one of those. If you have, your
> changelog utterly fails to explain why non of those are suitable and how
> your problem is special.
> 

I must agree. Propsed patch is a hack, and actually can make more trouble
to other subsystems. It is better to live with warning than perform
temporary lockdep off/on.

-- 
Witold Baryluk
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