linux-kernel - Re: [PATCH v2 1/1] headers: fix circular dependency between linux/sched.h and linux/wait.h

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Date:	Mon, 21 Feb 2011 18:29:39 +0200
From:	Felipe Balbi <balbi@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	David Cohen <dacohen@...il.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, linux-omap@...r.kernel.org,
	linux-media@...r.kernel.org, Alexey Dobriyan <adobriyan@...il.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v2 1/1] headers: fix circular dependency between
 linux/sched.h and linux/wait.h

Hi,

On Mon, Feb 21, 2011 at 05:20:45PM +0100, Peter Zijlstra wrote:
> > > I think Alexey already told you what you done wrong.
> > >
> > > Also, I really don't like the task_state.h header, it assumes a lot of
> > > things it doesn't include itself and only works because its using macros
> > > and not inlines at it probably should.
> > 
> > Like wait.h I'd say. The main issue is wait.h uses TASK_* macros but
> > cannot properly include sched.h as it would create a circular
> > dependency. So a file including wait.h is able to compile because the
> > dependency of sched.h relies on wake_up*() macros and it's not always
> > used.
> > We can still drop everything else from task_state.h but the TASK_*
> > macros and then the problem you just pointed out won't exist anymore.
> > What do you think about it?
> 
> I'd much rather see a real cleanup.. eg. remove the need for sched.h to
> include wait.h.

isn't that exactly what he's trying to achieve ? Moving TASK_* to its
own header is one approach, what other approach do you suggest ?

> afaict its needed because struct signal_struct and struct sighand_struct
> include a wait_queue_head_t. The inclusion seems to come through

yes.

> completion.h, but afaict we don't actually need to include completion.h
> because all we have is a pointer to a completion, which is perfectly
> fine with an incomplete type.

so maybe just dropping completion.h from sched.h would do it.

> This all would suggest we move the signal bits into their own header
> (include/linux/signal.h already exists and seems inviting).
> 
> And then make sched.c include signal.h and completion.h.

you wouldn't prevent the underlying problem which is the need to include
sched.h whenever you include wait.h and use wake_up*()

-- 
balbi
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