linux-kernel - Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg

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Date:	Tue, 15 Mar 2016 13:32:53 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to
 'xchg_or()'


* Ingo Molnar <mingo@...nel.org> wrote:

> But IMHO this really highlights a fundamental weakness of all this macro magic, 
> it's all way too fragile.
> 
> Why don't we introduce a boring family of APIs:
> 
> 	cmpxchg_8()
> 	cmpxchg_16()
> 	cmpxchg_32()
> 	cmpxchg_64()
> 
> 	xchg_or_32()
> 	xchg_or_64()
> 	...
> 
> ... with none of this pesky auto-typing property and none of the 
> macro-inside-a-macro crap? We could do clean types and would write them all in 
> proper C, not fragile CPP.
> 
> It's not like we migrate between the types all that frequently - and even if we 
> do, it's trivial.
> 
> hm?

So if we are still on the same page at this point, we'd have to add a pointer 
variant too I suspect:

	cmpxchg_ptr()
	xchg_ptr()

... whose bitness may differ between architectures(subarches), but it would still 
be a single variant per architecture, i.e. still with pretty clear type 
propagation and with a very clear notion of which architecture supports what.

It looks like a lot of work, but it's all low complexity work AFAICS that could be 
partly automated.

Thanks,

	Ingo