From: Catalin Marinas <catalin.marinas@arm.com>
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
jan sonnek <ha2nny@gmail.com>,
linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Andy Whitcroft <apw@shadowen.org>, Pavel Machek <pavel@ucw.cz>
Subject: Re: Regression - locking (all from 2.6.28)
Date: Mon, 16 Mar 2009 17:12:43 +0000 [thread overview]
Message-ID: <1237223563.19000.14.camel@pc1117.cambridge.arm.com> (raw)
In-Reply-To: <1236367186.10626.84.camel@nimitz>
Hi Dave,
> On Fri, 2009-03-06 at 18:00 +0000, Catalin Marinas wrote:
> > > I think you should be more worried about consistency rather than missing
> > > entries. Take these two lines of code:
> > >
> > > start_pfn = node->node_start_pfn;
> > > /* hotplug occurs here */
> > > end_pfn = start_pfn + node->node_spanned_pages;
> > >
> > > What if someone comes in and adds memory to the node, at the beginning
> > > of the node, after you have calculated start_pfn? Try to think of what
> > > value you'll get for end_pfn and whether it is consistent and was *ever*
> > > valid at all. Would that oops the kernel?
> >
> > I assume pfn_valid() should handle this and kmemleak wouldn't scan the
> > page, unless we need locks around pfn_valid as well but I haven't seen
> > any used in the kernel.
>
> You assume incorrectly. :(
>
> Take my above example, and assume that you have two nodes which are
> right next to each other. You might run over the end of one node and
> into the next one. Your pages will be pfn_valid() but you will be on
> the wrong node.
OK, thanks for taking the time to explain this. I currently added a
dependency on !MEMORY_HOTPLUG for kmemleak since holding the lock while
traversing the page structures is not really feasible.
> You could probably also use the memory hotplug mutex found here:
>
> https://lists.linux-foundation.org/pipermail/linux-pm/2008-November/018884.html
That would be a better option for kmemleak as well.
--
Catalin
next prev parent reply other threads:[~2009-03-16 17:14 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <49AC334A.9030800@gmail.com>
2009-03-02 20:11 ` Regression - locking (all from 2.6.28) Andrew Morton
2009-03-03 10:41 ` Catalin Marinas
2009-03-03 15:01 ` Catalin Marinas
2009-03-05 0:54 ` Dave Hansen
2009-03-05 18:04 ` Catalin Marinas
2009-03-05 18:29 ` Peter Zijlstra
2009-03-06 16:40 ` Catalin Marinas
2009-03-06 16:52 ` Dave Hansen
2009-03-06 17:18 ` Catalin Marinas
2009-03-06 17:26 ` Dave Hansen
2009-03-06 18:00 ` Catalin Marinas
2009-03-06 19:19 ` Dave Hansen
2009-03-06 19:28 ` Pavel Machek
2009-03-16 22:04 ` Rafael J. Wysocki
2009-03-17 0:07 ` KAMEZAWA Hiroyuki
2009-03-14 16:24 ` Pavel Machek
2009-03-16 17:12 ` Catalin Marinas [this message]
2009-03-03 18:12 ` Peter Zijlstra
2009-03-22 4:45 jan sonnek
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