linux-kernel - Re: [PATCH 2.6.21-rc5] MSI: read-flush MSI-X table

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Date:	Mon, 26 Mar 2007 17:09:51 -0700
From:	Greg KH <greg@...ah.com>
To:	Mitch Williams <mitch.a.williams@...el.com>,
	Michael Ellerman <michael@...erman.id.au>
Cc:	linux-pci@...ey.karlin.mff.cuni.cz, gregkh@...e.de,
	ebiederm@...ssion.com, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, auke-jan.h.kok@...el.com
Subject: Re: [PATCH 2.6.21-rc5] MSI: read-flush MSI-X table

On Mon, Mar 26, 2007 at 04:18:22PM -0700, Mitch Williams wrote:
> This patch fixes a kernel bug which is triggered when using the
> irqbalance daemon with MSI-X hardware.
> 
> Because both MSI-X interrupt messages and MSI-X table writes are posted,
> it's possible for them to cross while in-flight.  This results in
> interrupts being received long after the kernel thinks they're disabled,
> and in interrupts being sent to stale vectors after rebalancing.
> 
> This patch performs a read flush after writes to the MSI-X table for
> enable/disable and rebalancing operations.  Because this is an expensive
> operation, we do not perform the read flush after mask/unmask
> operations.  Hardware which supports MSI-X typically also supports some
> sort of interrupt moderation, so a read-flush is not necessary for
> mask/unmask operations.
> 
> This patch has been validated with (unreleased) network hardware which
> uses MSI-X.

How well does this play with the MSI core changes that Michael Ellerman
has proposed on the linux-pci mailing list?

thanks,

greg k-h
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