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Date: Wed, 6 Jun 2012 17:27:04 +0100
From: Matthew Garrett <mjg59@srcf.ucam.org>
To: Khalid Aziz <khalid.aziz@hp.com>
Cc: linux-kernel@vger.kernel.org, bhelgaas@google.com,
        linux-pci@vger.kernel.org
Subject: Re: [PATCH] Disable Bus Master on PCI device shutdown
Message-ID: <20120606162703.GA6779@srcf.ucam.org>
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On Wed, Jun 06, 2012 at 10:17:43AM -0600, Khalid Aziz wrote:

> That is a good piece of information. I see your concern and agree with
> it. My take is shutdown method for the drivers will end all active I/O
> and clear the I/O queue. This should take care of any DMA caused by an
> I/O request originating in the kernel. For devices like NIC, a DMA can
> be triggered by an incoming packet and I am trying to stop that by
> disabling Bus Master bit. This is the issue that was reported on kexec
> mailing list in July of last year and it involved qla driver. I observed
> similar problem with kexec on ia64 many years ago and had written a
> patch to disable Bus Master bit on kexec. This patch was in ia64 tree
> for some time before it was removed. HP shipped kernels with this patch
> for many years and those kernels have been in deployment in field for
> some 7+ years with no problems.

If the qla driver knows that this is safe, then can't this just be done 
in the qla driver?

-- 
Matthew Garrett | mjg59@srcf.ucam.org
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