Re: [PATCH v2 2/2] mm: compaction: fix the possible deadlock when isolating hugetlb pages

[Mel Gorman]

On Thu, Mar 16, 2023 at 07:06:47PM +0800, Baolin Wang wrote:
> 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>
> Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

-- 
Mel Gorman
SUSE Labs