linux-kernel - Re: [patch, -git] pcie hotplug bootup crash fix

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Date:	Mon, 26 May 2008 09:20:15 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>, drzeus-list@...eus.cx,
	kristen.c.accardi@...el.com
Subject: Re: [patch, -git] pcie hotplug bootup crash fix

On Monday, May 26, 2008 3:26 am Kenji Kaneshige wrote:
> Andrew Morton wrote:
> > On Mon, 26 May 2008 10:47:09 +0200 Ingo Molnar <mingo@...e.hu> wrote:
> >> * Kenji Kaneshige <kaneshige.kenji@...fujitsu.com> wrote:
> >>> I updated Ingo's patch. If it's ok, I'll send it to Jess Barnes with
> >>> some other patches for the other pciehp regression problems.
> >>
> >> looks good to me, thanks Kenji.
> >
> > It's a bit sad to add a large workaround like this.  I'm surprised
> > that fixing it properly is considered unviable for 2.6.26.  Normally
> > these fixes are pretty simple - just request the IRQ a bit later?
>
> Although I have not considered how to implement proper fix deeply,
> I don't think it's so simple. For example, current pciehp is doing
> like this:
>
> (1) some initialization
> (2) request_irq()
> (3) issue command
> (4) initialize slot data structure
>
> Maybe we want to do (2) after (4) to fix the problem. But if we
> simply move (2) after (4), we cannot detect the command completion
> event at (3) and it will cause command timeout.
>
> It's just an example, and there might be other things like this.
> This example might be fixed simply, but all my worry is that fixing
> this quickly might cause another regressions. This is why I think
> Ingo's approach is better in a short term.
>
> And another reason is I'm very nervous because I already caused
> many problems in pciehp since 2.6.26-rcX... :(

But you also fixed the problems, which is even more important! :)  I'm ok with 
the workaround for 2.6.26 as long as we can get a more proper fix into 
2.6.27.

Any thoughts, Kristen?

Thanks,
Jesse

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