linux-kernel - Re: [PATCH] PCI: Clear Bus Master bit only on kexec reboot

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Date:	Wed, 27 Nov 2013 15:18:09 -0700
From:	Khalid Aziz <khalid.aziz@...cle.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>,
	Greg KH <gregkh@...uxfoundation.org>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>, bhelgaas@...gle.com,
	cl91tp@...il.com, tianyu.lan@...el.com, khlebnikov@...nvz.org,
	gnomes@...rguk.ukuu.org.uk, indou.takao@...fujitsu.com,
	jility09@...il.com, f.otti@....at, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] PCI: Clear Bus Master bit only on kexec reboot

On 11/27/2013 03:07 PM, Matthew Garrett wrote:
> On Wed, Nov 27, 2013 at 02:01:06PM -0800, Greg KH wrote:
>> Anyway, I really don't care either way, but this seems like something
>> that the drivers should be doing.  What suddenly changed that caused
>> this problem to occur that hasn't happened in the years prior to now
>> that drives this to be a stable-kernel issue?
>
> We started clearing the busmaster bit on all devices on shutdown in
> 3.something in order to ensure that DMA wasn't occuring while we were
> in the process of performing a kexec. Some machines freeze on shutdown
> as a result. This patch reverts back to the original behaviour on real
> shutdown, while still avoiding the "This PCI device scribbled over my
> new kernel" kexec case.
>

Thanks for explaining this, Matthew. That was my reasoning exactly for 
why this patch should apply to stable. It fixes a real problem some 
users are experiencing. Commit log contains the URL to bugzilla entry 
for the problem.

--
Khalid
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