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mm/compaction: fix bug in hugetlb handling pathway

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The compaction code doesn't take references on pages until we're certain
we should attempt to handle it.

In the hugetlb case, isolate_or_dissolve_huge_page() may return -EBUSY
without taking a reference to the folio associated with our pfn.  If our
folio's refcount drops to 0, compound_nr() becomes unpredictable, making
low_pfn and nr_scanned unreliable.  The user-visible effect is minimal -
this should rarely happen (if ever).

Fix this by storing the folio statistics earlier on the stack (just like
the THP and Buddy cases).

Also revert commit 66fe1cf7f581 ("mm: compaction: use helper compound_nr
in isolate_migratepages_block") to make backporting easier.

Link: https://lkml.kernel.org/r/20250401021025.637333-1-vishal.moola@gmail.com
Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages")
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Vishal Moola (Oracle) 2025-03-31 19:10:24 -07:00 committed by Andrew Morton
parent 770c8d55c4
commit a84edd52f0
1 changed files with 3 additions and 3 deletions
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6
mm/compaction.c
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@ -981,13 +981,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
}
if (PageHuge(page)) {
const unsigned int order = compound_order(page);
/*
* skip hugetlbfs if we are not compacting for pages
* bigger than its order. THPs and other compound pages
* are handled below.
*/
if (!cc->alloc_contig) {
const unsigned int order = compound_order(page);
if (order <= MAX_PAGE_ORDER) {
low_pfn += (1UL << order) - 1;
@ -1011,8 +1011,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
/* Do not report -EBUSY down the chain */
if (ret == -EBUSY)
ret = 0;
low_pfn += compound_nr(page) - 1;
nr_scanned += compound_nr(page) - 1;
low_pfn += (1UL << order) - 1;
nr_scanned += (1UL << order) - 1;
goto isolate_fail;
}