linux-kernel - Re: [PATCH -v12 02/15] resources: Add probe

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Message-ID: <CAE9FiQUKxO5QmuaK5V1-rWzS98aRmyfDgC0Aonk-L5JRG1cd6A@mail.gmail.com>
Date:	Wed, 29 Aug 2012 08:57:56 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Tony Luck <tony.luck@...el.com>,
	David Miller <davem@...emloft.net>, x86 <x86@...nel.org>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH -v12 02/15] resources: Add probe_resource()

On Tue, Aug 28, 2012 at 5:10 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Tue, Aug 28, 2012 at 10:05 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> Ugh. Ok, looking closer at this,
>
> Btw, looking at that code, I also found what looks like a potential
> locking bug in allocate_resource().
>
> The code does
>
>     if (new->parent)
>        .. reallocate ..
>
> to check whether a resource was already allocated. HOWEVER, it does so
> without actually holding the resource lock. Which means that
> "new->parent" might in theory change.
>
> I don't really know if we care. Anybody who does a
> "allocate_resource()" on an existing resource that might already be in
> the resource tree hopefully does *not* do that in parallel with
> another user trying to change the resource allocation, so maybe the
> right thing to do is to just say "whatever, if there is a race with
> two threads reallocating the same resource at the same time, the bug
> is a much more serious one at a higher level".

yes, another patch that that split __allocate_resource out have the similar fix.

http://git.kernel.org/?p=linux/kernel/git/yinghai/linux-yinghai.git;a=commitdiff;h=5d52b21303b7271ba4c5302b387766628f074ae2

but the changelog does not that mention the reason.

also have another version for probe_resource, please check attached version -v8.

Thanks

Yinghai

Download attachment "probe_resource_2.patch" of type "application/octet-stream" (7896 bytes)