linux-kernel - Re: [PATCH V2] lglock: add read-preference local-global rwlock

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Message-ID: <CANN689F6RHCtDAiBGu=n60UKUEE5Ld50gkwS3rNdE2GN2+v3nA@mail.gmail.com>
Date:	Mon, 4 Mar 2013 17:37:09 -0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Lai Jiangshan <eag0628@...il.com>, linux-doc@...r.kernel.org,
	peterz@...radead.org, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, namhyung@...nel.org,
	mingo@...nel.org, linux-arch@...r.kernel.org,
	linux@....linux.org.uk, xiaoguangrong@...ux.vnet.ibm.com,
	wangyun@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	rusty@...tcorp.com.au, rostedt@...dmis.org, rjw@...k.pl,
	vincent.guittot@...aro.org, tglx@...utronix.de,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
	sbw@....edu, tj@...nel.org, akpm@...ux-foundation.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH V2] lglock: add read-preference local-global rwlock

On Sun, Mar 3, 2013 at 9:40 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>> However, I still think that FALLBACK_BASE only adds the unnecessary
>> complications. But even if I am right this is subjective of course, please
>> feel free to ignore.

Would it help if I sent out that version (without FALLBACK_BASE) as a
formal proposal ?

> Hmm. But then I do not understand the lglock annotations. Obviously,
> rwlock_acquire_read() in lg_local_lock() can't even detect the simplest
> deadlock, say, lg_local_lock(LOCK) + lg_local_lock(LOCK). Not to mention
> spin_lock(X) + lg_local_lock(Y) vs lg_local_lock(Y) + spin_lock(X).
>
> OK, I understand that it is not easy to make these annotations correct...

I am going to send out a proposal to fix the existing lglock
annotations and detect the two cases you noticed. It's actually not
that hard :)

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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