linux-kernel - Re: Sleeping in RCU list traversal

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Message-Id: <200710080156.IFB56934.tHMLFFJSFOVOOQ@I-love.SAKURA.ne.jp>
Date:	Mon, 8 Oct 2007 01:56:30 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	junwang1234@...il.com, a.p.zijlstra@...llo.nl
Cc:	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: Sleeping in RCU list traversal

Hello.

Jun WANG wrote:
> I'm sorry,I think I got your idea, if you do not need ptr in
> my_task_that_may_sleep(), why you need to grab a reference to "ptr". If
> your my_task_that_may_sleep() needs ptr, and according to the 
> "memory region pointed by "ptr" never be removed." you say,
> it is ok to use "ptr" after rcu_read_ulock(). The basic idea behind RCU
> is to split updates into "removal" and "reclamation" phases. If you
> memory region pointed by "ptr" will not "reclamation" in sleep, it is ok
I need "ptr" in my_task_that_may_sleep(), but regarding my case,
memory region pointed by "ptr" will never be kfree()ed.

So, I don't need to grab a reference to "ptr"
because memory region pointed by "ptr" will never be kfree()ed.
And it is legal to use "ptr" after rcu_read_unlock()
because memory region pointed by "ptr" will never be kfree()ed.

Thank you.

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