Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg_or()'

From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Peter Zijlstra" <a.p.zijlstra@chello.nl>,
	"Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg_or()'
Date: Tue, 15 Mar 2016 13:32:53 +0100	[thread overview]
Message-ID: <20160315123253.GA10152@gmail.com> (raw)
In-Reply-To: <20160315120147.GA9742@gmail.com>

* Ingo Molnar <mingo@kernel.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