linux-kernel - Re: [patch 2/6] epoll keyed wakeups v2 - introduce new *

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Message-ID: <alpine.DEB.1.10.0902031216490.23050@alien.or.mcafeemobile.com>
Date:	Tue, 3 Feb 2009 12:24:09 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>
Subject: Re: [patch 2/6] epoll keyed wakeups v2 - introduce new *_poll()
 wakeup macros

On Tue, 3 Feb 2009, Andrew Morton wrote:

> On Tue, 3 Feb 2009 11:20:46 -0800 (PST)
> Davide Libenzi <davidel@...ilserver.org> wrote:
> 
> > On Tue, 3 Feb 2009, Davide Libenzi wrote:
> > 
> > > On Tue, 3 Feb 2009, Andrew Morton wrote:
> > > 
> > > > On Sun, 01 Feb 2009 12:04:23 -0800 Davide Libenzi <davidel@...ilserver.org> wrote:
> > > > 
> > > > > +#define wake_up_nested_poll(x, m, s)					\
> > > > > +do {									\
> > > > > +	unsigned long flags;						\
> > > > > +									\
> > > > > +	spin_lock_irqsave_nested(&(x)->lock, flags, (s));		\
> > > > > +	wake_up_locked_poll(x, m);					\
> > > > > +	spin_unlock_irqrestore(&(x)->lock, flags);			\
> > > > > +} while (0)
> > > > 
> > > > I had to go and find the callsite to work out the type of `x' :(
> > > > 
> > > > - this macro can be passed the address of any structure which has a
> > > >   `spinlock_t lock;' in it, which seems strange.
> > > > 
> > > > - It references its first arg three times.
> > > > 
> > > > Is there any reason why we can't implement this in C?  
> > > 
> > > I don't see any reason why these two couldn't be normal functions (I 
> > > just referenced wake_up_nested(), that was a macro in the first place). 
> > 
> > Actually reading the comments helps :) It triggers an include-hell, if you 
> > make them inline. Since they're lockdep debug thingies, I think it's kinda 
> > wasted turn them into non-inline real functions, so they'd better remain 
> > macros IMO.
> > 
> 
> ho hum.  I think it'd be worth at least renaming the arguments to
> something less daft, for readability reasons.
> 
> One could also do
> 
> do {
> 	wait_queue_head_t *__wqh = x;
> 	<use __wqh>
> }
> 
> which would provide typechecking of the first arg (so people can no
> longer "pass the address of any structure which has a `spinlock_t
> lock;' in it") and which fixes the multiple-references-to-an-argument
> issue.

OK, you've got my arg-rename bits already. Another version using a 
typecheck() in there? Or you prefer the explicit instantiation?


- Davide


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