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

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Message-Id: <7ab3bffebe59fb419234a68dec1e4572a2518563.1678962352.git.baolin.wang@linux.alibaba.com>
Date:   Thu, 16 Mar 2023 19:06:47 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     akpm@...ux-foundation.org
Cc:     mgorman@...hsingularity.net, osalvador@...e.de, vbabka@...e.cz,
        william.lam@...edance.com, mike.kravetz@...cle.com,
        baolin.wang@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] 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.

Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages")
Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
---
Changes from v1:
 - Collect reviewed tags. Thanks Mike and Vlastimil.
---
 mm/compaction.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/compaction.c b/mm/compaction.c
index 7e645cdfc2e9..3df076716691 100644
--- a/mm/compaction.c
+++ b/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);

 			/*
-- 
2.27.0