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

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Date:	Wed, 27 Nov 2013 13:22:27 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Khalid Aziz <khalid.aziz@...cle.com>
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, mjg59@...f.ucam.org,
	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 Wed, Nov 27, 2013 at 12:59:40PM -0700, Khalid Aziz wrote:
> On 11/27/2013 12:38 PM, ebiederm@...ssion.com wrote:
> >Khalid Aziz <khalid.aziz@...cle.com> writes:
> >
> >>Add a flag to tell the PCI subsystem that kernel is shutting down
> >>in prepapration to kexec a kernel. Add code in PCI subsystem to use
> >>this flag to clear Bus Master bit on PCI devices only in case of
> >>kexec reboot. This fixes https://bugzilla.kernel.org/show_bug.cgi?id=63861
> >>and avoids any other issues caused by clearing Bus Master bit on PCI
> >>devices in normal shutdown path. This patch is based on discussion at
> >>http://marc.info/?l=linux-pci&m=138425645204355&w=2
> >
> >Scratches head.
> >
> >Given that most devices already call pci_disable_device which clears the
> >bus master bit how does this change anything meaningful?
> >
> >Is is the problem here that most drivers are lazy and have a noop
> >shutdown method?
> 
> Yes, that is exactly the problem.

Then fix the drivers please.  It's not as if you don't have access to
the source for them all...

greg k-h
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