mm: compaction: fix the possible deadlock when isolating hugetlb pages

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.

Link: https://lkml.kernel.org/r/7ab3bffebe59fb419234a68dec1e4572a2518563.1678962352.git.baolin.wang@linux.alibaba.com
Fixes: 369fa22 ("mm: make alloc_contig_range handle free hugetlb pages")
Signed-off-by: Baolin Wang <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Reviewed-by: Mike Kravetz <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: William Lam <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Baolin Wang

mm/compaction.c

@@ -894,6 +894,11 @@ 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);
 
 			/*