Messages in this thread | | | Date | Tue, 17 Mar 2009 09:07:32 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: Regression - locking (all from 2.6.28) |
| |
On Mon, 16 Mar 2009 23:04:27 +0100 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> On Friday 06 March 2009, Pavel Machek wrote: > > 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. > > Yes. In fact, sending the patch again to me would be appreciated. >
Ah...but as I wrote, for me, testing this is difficult. Could some expert of hibernation update and post this again ? For memoyr hotplug. it seems enough that sending the patch witch CC: to linux-mm and including "Memory Hotplug" in the subject.
Thanks, -Kame
| |