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From: Florian Weimer <fweimer@redhat.com>
To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: 'GNU C Library' <libc-alpha@sourceware.org>
Subject: Re: [PATCH] malloc: Use correct C11 atomics for fastbin
References: <PAWPR08MB8982002BD1E5CE0E74F4F19B830A9@PAWPR08MB8982.eurprd08.prod.outlook.com>
Date: Mon, 21 Nov 2022 17:18:40 +0100
In-Reply-To: <PAWPR08MB8982002BD1E5CE0E74F4F19B830A9@PAWPR08MB8982.eurprd08.prod.outlook.com>
	(Wilco Dijkstra's message of "Mon, 21 Nov 2022 16:09:05 +0000")
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* Wilco Dijkstra:

> Fix memory ordering issues in the fastbin implementation: in REMOVE_FB the
> next pointer is read before any MO synchronization, however in the C11 atomic
> model this is only correct after a load acquire. Refactor the fastbin code
> and add a dedicated fastbin_push/pop implementation. The number of acquire
> or release atomics remains the same, and the new functions are inlined, so
> performance is unaffected.
>
> Passes regress, OK for commit?

Did you actually observe any problems resulting from this?  We
previously concluded that the dependency chain would mae this valid
(outside the C11 memory model).

Thanks,
Florian