When trying to isolate a migratable pageblock, it can contain several
normal pages or several hugetlb pages (e.g. CONT-PTE 64K hugetlb on arm64)
in a pageblock. That means we may hold the lru lock of a normal page to
continue to isolate the next hugetlb page by isolate_or_dissolve_huge_page()
in the same migratable pageblock.
However in the isolate_or_dissolve_huge_page(), it may allocate a new hugetlb
page and dissolve the old one by alloc_and_dissolve_hugetlb_folio() if the
hugetlb's refcount is zero. That means we can still enter the direct compaction
path to allocate a new hugetlb page under the current lru lock, which
may cause possible deadlock.
To avoid this possible deadlock, we should release the lru lock when trying
to isolate a hugetbl page. Moreover it does not make sense to take the lru
lock to isolate a hugetlb, which is not in the lru list.
Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages")
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/mm/compaction.c b/mm/compaction.c
index c9d9ad958e2a..ac8ff152421a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -893,6 +893,11 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
}
if (PageHuge(page) && cc->alloc_contig) {
+ if (locked) {
+ unlock_page_lruvec_irqrestore(locked, flags);
+ locked = NULL;
+ }
+
ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
/*
--
2.27.0
