linux-kernel - Re: [PATCH 46/50] preempt.h: Kill dependency on list.h

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Message-ID: <20231217020545.op7znnvvoy4lthxw@moria.home.lan>
Date: Sat, 16 Dec 2023 21:05:45 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	tglx@...utronix.de, x86@...nel.org, tj@...nel.org,
	peterz@...radead.org, mathieu.desnoyers@...icios.com,
	paulmck@...nel.org, keescook@...omium.org,
	dave.hansen@...ux.intel.com, mingo@...hat.com, will@...nel.org,
	longman@...hat.com, boqun.feng@...il.com, brauner@...nel.org
Subject: Re: [PATCH 46/50] preempt.h: Kill dependency on list.h

On Sat, Dec 16, 2023 at 06:03:36PM -0800, Randy Dunlap wrote:
> 
> 
> On 12/16/23 16:20, Kent Overstreet wrote:
> > On Sun, Dec 17, 2023 at 12:18:17AM +0000, Matthew Wilcox wrote:
> >> On Sat, Dec 16, 2023 at 04:04:43PM -0800, Randy Dunlap wrote:
> >>>
> >>>
> >>> On 12/16/23 14:35, Kent Overstreet wrote:
> >>>> On Sat, Dec 16, 2023 at 06:13:41AM +0000, Matthew Wilcox wrote:
> >>>>> On Fri, Dec 15, 2023 at 10:35:47PM -0500, Kent Overstreet wrote:
> >>>>>> -	INIT_HLIST_NODE(&notifier->link);
> >>>>>> +	/* INIT_HLIST_NODE() open coded, to avoid dependency on list.h */
> >>>>>> +	notifier->link.next = NULL;
> >>>>>> +	notifier->link.pprev = NULL;
> >>>>>
> >>>>> Arguably INIT_HLIST_NODE() belongs in types.h -- we already have
> >>>>> RCUREF_INIT() and ATOMIC_INIT() in there.
> >>>>
> >>>> I think I'd prefer to keep types.h as minimal as possible - as soon as
> >>>> we start putting non type stuff in there people won't know what the
> >>>> distinction is and it'll grow.
> >>>>
> >>>> preempt.h is a bit unusual too, normally we'd just split out a _types.h
> >>>> header there but it's not so easy to split up usefully.
> >>>>
> >>>
> >>> I don't feel like I have NAK power, but if I did, I would NAK
> >>> open coding of INIT_HLIST_HEAD() or anything like it.
> >>> I would expect some $maintainer to do likewise, but I could be
> >>> surprised.
> >>
> >> There is another solution here (although I prefer moving INIT_HLIST_HEAD
> >> into types.h).  The preprocessor allows redefinitions as long as the two
> >> definitions match exactly.  So you can copy INIT_HLIST_HEAD into
> >> preempt.h and if the definition ever changes, we'll notice.
> > 
> > I like it.
> 
> Possible to revert 490d6ab170c9 ? although with something list
> this inserted:
> 
> 	struct hlist_node *_p = h;
> and then use _p instead of h (or the old macro's 'ptr')
> 
> The code looks the same to me, although I could have mucked something
> up:     https://godbolt.org/z/z76nsqGx3
> 
> although Andrew prefers inlines for type checking.

I prefer inlines whenever possible too, a macro should really be a
signal that 'something interesting is going on here'.

I'm just going with my original version.