+ mm-compaction-fix-the-possible-deadlock-when-isolating-hugetlb-pages.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: compaction: fix the possible deadlock when isolating hugetlb pages
has been added to the -mm mm-unstable branch.  Its filename is
     mm-compaction-fix-the-possible-deadlock-when-isolating-hugetlb-pages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-compaction-fix-the-possible-deadlock-when-isolating-hugetlb-pages.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Baolin Wang <baolin.wang@linux.alibaba.com>
Subject: mm: compaction: fix the possible deadlock when isolating hugetlb pages
Date: Thu, 16 Mar 2023 19:06:47 +0800

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: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: William Lam <william.lam@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/mm/compaction.c~mm-compaction-fix-the-possible-deadlock-when-isolating-hugetlb-pages
+++ a/mm/compaction.c
@@ -894,6 +894,11 @@ isolate_migratepages_block(struct compac
 		}
 
 		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);
 
 			/*
_

Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are

mm-compaction-consider-the-number-of-scanning-compound-pages-in-isolate-fail-path.patch
mm-compaction-fix-the-possible-deadlock-when-isolating-hugetlb-pages.patch