Messages in this thread | | | Date | Fri, 6 Mar 2009 20:28:12 +0100 | From | Pavel Machek <> | Subject | Re: Regression - locking (all from 2.6.28) |
| |
Hi!
On Fri 2009-03-06 11:19:46, Dave Hansen wrote: > 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. > > Please take a look at those locks that I mentioned. Notice that they > are lock the pgdat *span*, not the validity of pages inside the pgdat. > Your code deals with what pages the pgdats *span* and thus needs that > lock. Notice that my example also had to do with those two lines of > code incorrectly guessing the pgdat's *span*. > > We recently went to some pain to make sure that the software suspend > code (which walks pgdat ranges as well) worked with memory hotplug. > There really isn't that much code around that actually cares at runtime > about which physical areas a particular node or zone spans. Yours is a > rarity and will require some caution. > > You could probably also use the memory hotplug mutex found here: > > https://lists.linux-foundation.org/pipermail/linux-pm/2008-November/018884.html > > But I'm not sure where those patches have gone. Hmmm. Pavel?
I don't think they were applied. They probably should... Rafael was about to look into that, but he lost the patch pointer. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
| |