linux-kernel - Re: [PATCH v2 2/7] iommu: IOMMU Groups

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Date:	Thu, 21 Jun 2012 10:07:34 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	joerg.roedel@....com, dwmw2@...radead.org,
	iommu@...ts.linux-foundation.org, bhelgaas@...gle.com,
	aik@...abs.ru, david@...son.dropbear.id.au, konrad.wilk@...cle.com,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	gregkh@...uxfoundation.org, ddutile@...hat.com, liuj97@...il.com
Subject: Re: [PATCH v2 2/7] iommu: IOMMU Groups

On Wed, 2012-06-20 at 10:48 -0600, Alex Williamson wrote:

> Yes, I was assuming the caller held a reference to the struct device to
> prevent such a race, looks like I forgot to document that in the
> comments.  I'll have to think about if we can fix the ordering problem.
> We can re-order the list_add vs notification, but then we just risk
> dropping the remove.  Perhaps we need to extend the lock or add another
> to group {list add, notify add}, {list lookup, remove, notify remove}.
> I'm not even sure this race is possible though w/ a device reference.

Or we put the burden on the callers not to racily add & remove,
including full completion of related notifiers. Might not even be hard
(ie might already be the case).

Cheers,
Ben.


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