On Mon, 7 Jul 2014, Johannes Weiner wrote: > Hugh reports: > > VM_BUG_ON_PAGE(!(pc->flags & PCG_MEM)) > mm/memcontrol.c:6680! > page had count 1 mapcount 0 mapping anon index 0x196 > flags locked uptodate reclaim swapbacked, pcflags 1, memcg not root > mem_cgroup_migrate < move_to_new_page < migrate_pages < compact_zone < > compact_zone_order < try_to_compact_pages < __alloc_pages_direct_compact < > __alloc_pages_nodemask < alloc_pages_vma < do_huge_pmd_anonymous_page < > handle_mm_fault < __do_page_fault > > mem_cgroup_migrate() assumes that a page is only migrated once and > then freed immediately after. > > However, putting the page back on the LRU list and dropping the > isolation refcount is not done atomically. This allows a PFN-based > migrator like compaction to isolate the page, see the expected > anonymous page refcount of 1, and migrate the page once more. > > Catch pages that have already been migrated and abort migration > gracefully. > > Reported-by: Hugh Dickins <hughd@xxxxxxxxxx> > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > --- > mm/memcontrol.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 1e3b27f8dc2f..e4afdbdda0a7 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6653,7 +6653,10 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage, > if (!PageCgroupUsed(pc)) > return; > > - VM_BUG_ON_PAGE(!(pc->flags & PCG_MEM), oldpage); > + /* Already migrated */ > + if (!(pc->flags & PCG_MEM)) > + return; > + I am curious why you chose to fix the BUG in this way, instead of - pc->flags &= ~(PCG_MEM | PCG_MEMSW); + pc->flags = 0; a few lines further down. The page that gets left behind with just PCG_USED is anomalous (for an LRU page, maybe not for a kmem page), isn'it it? And liable to cause other problems. For example, won't it go the wrong way in the "Surreptitiously" test in mem_cgroup_page_lruvec(): the page no longer has a hold on any memcg, so is in a danger of being placed on a gone-memcg's LRU? Hugh > VM_BUG_ON_PAGE(do_swap_account && !(pc->flags & PCG_MEMSW), oldpage); > pc->flags &= ~(PCG_MEM | PCG_MEMSW); > > -- > 2.0.0 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>