linux-kernel - Re: [PATCH] lockdep: Add a document describing crossrelease feature

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Message-ID: <20160706053328.GB2279@X58A-UD3R>
Date:	Wed, 6 Jul 2016 14:33:29 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Boqun Feng <boqun.feng@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, walken@...gle.com
Subject: Re: [PATCH] lockdep: Add a document describing crossrelease feature

On Wed, Jul 06, 2016 at 11:17:10AM +0900, Byungchul Park wrote:
> 
> lock(A)
> wait_for(B)
> ~~~~~~~~~~~~~~~~~~~~~~~~ <- serialized by atomic operation
> 		lock(A)
> 		unlock(A)
> 		wake(B)
> unlock(A)

By the way, I have a question. Is there anyone who could answer it?

I want to serialize between two context's lock operations, for example,

	context A	context B
	--------------	--------------
	lock A
	lock B		...
	lock C
	atomic_inc_return
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ <- serialization
			atomic_read
			lock D
	...		lock E
			lock F

so that we can see these in the order like A -> B -> C -> D -> E -> F.

atomic_inc_return() is used after lock C in context A, and atomic_read()
is used before lock D in context B. And I want to make it serialized when
the atomic_read() can see the increased value.

Can I use smp_mb__after_atomic() just after atomic_read() or should I use
smp_mb()? I think anyway I have to choose one of them for that ordering.

Thank you,
Byungchul