Compaction always operates on pages from a single given zone when isolating both pages to migrate and freepages. Pageblock boundaries are intersected with zone boundaries to be safe in case zone starts or ends in the middle of pageblock. The use of pageblock_pfn_to_page() protects against non-contiguous pageblocks.

The functions fast_isolate_freepages() and fast_isolate_around() don't currently protect the fast freepage isolation thoroughly enough against these corner cases, and can result in freepage isolation operate outside of zone boundaries:

- in fast_isolate_freepages() if we get a pfn from the first pageblock of a zone that starts in the middle of that pageblock, 'highest' can be a pfn outside of the zone. If we fail to isolate anything in this function, we may then call fast_isolate_around() on a pfn outside of the zone and there effectively do a set_pageblock_skip(page_to_pfn(highest)) which may currently hit a VM_BUG_ON() in some configurations - fast_isolate_around() checks only the zone end boundary and not beginning, nor that the pageblock is contiguous (with pageblock_pfn_to_page()) so it's possible that we end up calling isolate_freepages_block() on a range of pfn's from two different zones and end up e.g. isolating freepages under the wrong zone's lock.

This patch should fix the above issues.

Fixes: 5a811889de10 ("mm, compaction: use free lists to quickly locate a migration target") Cc: stable@vger.kernel.org Signed-off-by: Vlastimil Babka vbabka@suse.cz --- mm/compaction.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-)

Hi, as promised here's a fix for issues that I think exist regardless of the memblock stuff, but were partially exposed by that. I will see if I can manage to test that it does prevent the known symptoms (it should if I didn't miss anything).

diff --git a/mm/compaction.c b/mm/compaction.c index 190ccdaa6c19..22a35521e358 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1288,7 +1288,7 @@ static void fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated) { unsigned long start_pfn, end_pfn; - struct page *page = pfn_to_page(pfn); + struct page *page;

/* Do not search around if there are enough pages already */ if (cc->nr_freepages >= cc->nr_migratepages) @@ -1299,8 +1299,12 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long return;

/* Pageblock boundaries */ - start_pfn = pageblock_start_pfn(pfn); - end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)) - 1; + start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn); + end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)); + + page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone); + if (!page) + return;

/* Scan before */ if (start_pfn != pfn) { @@ -1402,7 +1406,8 @@ fast_isolate_freepages(struct compact_control *cc) pfn = page_to_pfn(freepage);

if (pfn >= highest) - highest = pageblock_start_pfn(pfn); + highest = max(pageblock_start_pfn(pfn), + cc->zone->zone_start_pfn);

if (pfn >= low_pfn) { cc->fast_search_fail = 0; @@ -1472,7 +1477,8 @@ fast_isolate_freepages(struct compact_control *cc) } else { if (cc->direct_compaction && pfn_valid(min_pfn)) { page = pageblock_pfn_to_page(min_pfn, - pageblock_end_pfn(min_pfn), + min(pageblock_end_pfn(min_pfn), + zone_end_pfn(cc->zone)), cc->zone); cc->free_pfn = min_pfn; }