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

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Message-ID: <20160315131748.GY6344@twins.programming.kicks-ass.net>
Date:	Tue, 15 Mar 2016 14:17:48 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to
 'xchg_or()'

On Tue, Mar 15, 2016 at 01:32:53PM +0100, Ingo Molnar wrote:
> 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()

We typically call those _long(), like atomic_long_t etc.. Under the
assumption that sizeof(long) == sizeof(void *).

Also, _IF_ we're going to do this, this is the perfect opportunity to
also introduce the __atomic address space and load() and store()
operations. This is needed for architectures where:

	cmpxchg()/xchg()

isn't safe against regular stores, like all those who implement atomics
using hashed spinlocked.

Its going to be a horrid lot of work though :/