linux-kernel - Re: [PATCH v2] PCI: fix pci_bus_alloc_resource() hang, prefer positive decode

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Message-ID: <20101112151737.GC28968@aftab>
Date:	Fri, 12 Nov 2010 16:17:37 +0100
From:	Borislav Petkov <bp@...64.org>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Bob Picco <bpicco@...hat.com>,
	Brian Bloniarz <phunge0@...mail.com>,
	Charles Butterfield <charles.butterfield@...tcentury.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"Horst H. von Brand" <vonbrand@....utfsm.cl>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefan Becker <chemobejk@...il.com>,
	Chuck Ebbert <cebbert@...hat.com>,
	Fabrice Bellet <fabrice@...let.info>,
	Yinghai Lu <yinghai@...nel.org>,
	Leann Ogasawara <leann.ogasawara@...onical.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] PCI: fix pci_bus_alloc_resource() hang, prefer
 positive decode

On Wed, Nov 10, 2010 at 12:26:07PM -0500, Bjorn Helgaas wrote:
> 
> When a PCI bus has two resources with the same start/end, e.g.,
> 
>     pci_bus 0000:04: resource 2 [mem 0xd0000000-0xd7ffffff pref]
>     pci_bus 0000:04: resource 7 [mem 0xd0000000-0xd7ffffff]
> 
> the previous pci_bus_find_resource_prev() implementation would alternate
> between them forever:
> 
>     pci_bus_find_resource_prev(... [mem 0xd0000000-0xd7ffffff pref])
>         returns [mem 0xd0000000-0xd7ffffff]
>     pci_bus_find_resource_prev(... [mem 0xd0000000-0xd7ffffff])
>         returns [mem 0xd0000000-0xd7ffffff pref]
>     pci_bus_find_resource_prev(... [mem 0xd0000000-0xd7ffffff pref])
>         returns [mem 0xd0000000-0xd7ffffff]
>     ...
> 
> This happened because there was no ordering between two resources with the
> same start and end.  A resource that had the same start and end as the
> cursor, but was not itself the cursor, was considered to be before the
> cursor.
> 
> This patch fixes the hang by making a fixed ordering between any two
> resources.
> 
> In addition, it tries to allocate from positively decoded regions before
> using any subtractively decoded resources.  This means we will use a
> positive decode region before a subtractive decode one, even if it means
> using a smaller address.
> 
> Reference: https://bugzilla.kernel.org/show_bug.cgi?id=22062
> Signed-off-by: Bjorn Helgaas <bjorn.helgaas@...com>

Looks good.

Reported-and-tested-by: Borislav Petkov <bp@...64.org>

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
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