On Wed, 28 Apr 2010 00:32:42 +0200 Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > On Tue, Apr 27, 2010 at 05:27:36PM -0500, Christoph Lameter wrote: > > Can we simply wait like in the fault path? > > There is no bug there, no need to wait either. I already audited it > before, and I didn't see any bug. Unless you can show a bug with CPU A > running the rmap_walk on process1 before process2, there is no bug to > fix there. > I think there is no bug, either. But that safety is fragile. > > > > > Patch 3 notes that while a VMA is moved under the anon_vma lock, the page > > > tables are not similarly protected. Where migration PTEs are > > > encountered, they are cleaned up. > > > > This means they are copied / moved etc and "cleaned" up in a state when > > the page was unlocked. Migration entries are not supposed to exist when > > a page is not locked. > > patch 3 is real, and the first thought I had was to lock down the page > before running vma_adjust and unlock after move_page_tables. But these > are virtual addresses. Maybe there's a simpler way to keep migration > away while we run those two operations. > Doing some check in move_ptes() after vma_adjust() is not safe. IOW, when vma's information and information in page-table is incosistent...objrmap is broken and migartion will cause panic. Then...I think there are 2 ways. 1. use seqcounter in "mm_struct" as previous patch and lock it at mremap. or 2. get_user_pages_fast() when do remap. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>