Messages in this thread | | | Subject | Re: Regression - locking (all from 2.6.28) | From | Catalin Marinas <> | Date | Mon, 16 Mar 2009 17:12:43 +0000 |
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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
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