linux-kernel - Re: [PATCH] workqueue: Fix alignment calculation in alloc

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Message-ID: <3487.1288043213@redhat.com>
Date:	Mon, 25 Oct 2010 22:46:53 +0100
From:	David Howells <dhowells@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	dhowells@...hat.com, akpm@...ux-foundation.org,
	Tejun Heo <tj@...nel.org>, linux-am33-list@...hat.com,
	linux-kernel@...r.kernel.org,
	Akira Takeuchi <takeuchi.akr@...panasonic.com>,
	Mark Salter <msalter@...hat.com>
Subject: Re: [PATCH] workqueue: Fix alignment calculation in alloc_cwqs()

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> No it doesn't. Those bits really require that many bytes of alignment.
> 
> Think about it: if the low 8 bits of the pointer are used for flags,
> then the actual pointer itself needs to be aligned to a 256-byte
> boundary.
> 
> So the code is right. If needs to ask for "1 << WORK_STRUCT_FLAG_BITS"
> alignment, and if it doesn't get it (because the allocator is somehow
> broken - percpu allocator issues?), things will break.

That's a good point.

David
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