linux-kernel - Re: [PATCH] Export current_is

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Message-ID: <Pine.LNX.4.64.0612070846550.3615@woody.osdl.org>
Date:	Thu, 7 Dec 2006 08:49:02 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Andrew Morton <akpm@...l.org>
cc:	David Howells <dhowells@...hat.com>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Roland Dreier <rdreier@...co.com>,
	Andy Fleming <afleming@...escale.com>,
	Ben Collins <ben.collins@...ntu.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>
Subject: Re: [PATCH] Export current_is_keventd() for libphy



On Wed, 6 Dec 2006, Andrew Morton wrote:
>
> But this will return to the caller if the callback is presently running on
> a different CPU.  The whole point here is to be able to reliably kill off
> the pending work so that the caller can free resources.

I mentioned that in one of the emails.

We do not _have_ the information to not do that. It simply doesn't exist. 
We can either wait for _all_ pending entries on the to complete (by 
waiting for the workqueue counters for added/removed to be the same), or 
we can have the race.

> Also, I worry that this code can run the callback on the caller's CPU. 

Right.

> Users of per-cpu workqueues can legitimately assume that each callback runs
> on the right CPU.

Not if they use this interface, they can't.

They asked for it, they get it. That's the unix philosophy. 

		Linus
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