Hi Mel, > Still travelling and am not in a position to test this properly :(. > However, this bug feels very similar to a bug in the migration scanner where > a pfn_valid check is missed because the start is not aligned. Henrik, when > did this start happening? I would be a little surprised if it started between > 3.6 and 3.7-rcX but maybe it's just easier to hit now for some reason. I started using transparent hugepages when moving to 3.7-rc1, so it is quite possible that the problem was there already in 3.6. > How reproducible is this? Is there anything in particular you do to > trigger the oops? Unfortunately nothing special, and it is rare. IIRC, it has happened after a long uptime, but I guess that only means the probability of the oops is higher then. > Does the following patch help any? It's only compile tested I'm afraid. > > ---8<--- > mm: compaction: check pfn_valid when entering a new MAX_ORDER_NR_PAGES block during isolation for free > > Commit 0bf380bc (mm: compaction: check pfn_valid when entering a new > MAX_ORDER_NR_PAGES block during isolation for migration) added a check > for pfn_valid() when isolating pages for migration as the scanner does > not necessarily start pageblock-aligned. However, the free scanner has > the same problem. If it encounters a hole, it can also trigger an oops > when is calls PageBuddy(page) on a page that is within an hole. > > Reported-by: Henrik Rydberg <rydberg@xxxxxxxxxxx> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > --- > mm/compaction.c | 10 ++++++++++ > 1 files changed, 10 insertions(+), 0 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 9eef558..7d85ad485 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -298,6 +298,16 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, > continue; > if (!valid_page) > valid_page = page; > + > + /* > + * As blockpfn may not start aligned, blockpfn->end_pfn > + * may cross a MAX_ORDER_NR_PAGES boundary and a pfn_valid > + * check is necessary. If the pfn is not valid, stop > + * isolation. > + */ > + if ((blockpfn & (MAX_ORDER_NR_PAGES - 1)) == 0 && > + !pfn_valid(blockpfn)) > + break; > if (!PageBuddy(page)) > continue; > I am running with it now, adding a printout to see if the case happens at all. Might take a while, will try to stress the machine a bit. Thanks, Henrik -- 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>