mm: migrate: fix THP's mapcount on isolation
[ Upstream commit 829ae0f81ce093d674ff2256f66a714753e9ce32 ]
The issue is reported when removing memory through virtio_mem device. The
transparent huge page, experienced copy-on-write fault, is wrongly
regarded as pinned. The transparent huge page is escaped from being
isolated in isolate_migratepages_block(). The transparent huge page can't
be migrated and the corresponding memory block can't be put into offline
state.
Fix it by replacing page_mapcount() with total_mapcount(). With this, the
transparent huge page can be isolated and migrated, and the memory block
can be put into offline state. Besides, The page's refcount is increased
a bit earlier to avoid the page is released when the check is executed.
Link: https://lkml.kernel.org/r/20221124095523.31061-1-gshan@redhat.com
Fixes: 1da2f328fa64 ("mm,thp,compaction,cma: allow THP migration for CMA allocations")
Signed-off-by: Gavin Shan <gshan@redhat.com>
Reported-by: Zhenyu Zhang <zhenyzha@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org> [5.7+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/mm/compaction.c b/mm/compaction.c
index b6bd745..e8fcf0e 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -993,22 +993,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
}
/*
- * Migration will fail if an anonymous page is pinned in memory,
- * so avoid taking lru_lock and isolating it unnecessarily in an
- * admittedly racy check.
- */
- mapping = page_mapping(page);
- if (!mapping && page_count(page) > page_mapcount(page))
- goto isolate_fail;
-
- /*
- * Only allow to migrate anonymous pages in GFP_NOFS context
- * because those do not depend on fs locks.
- */
- if (!(cc->gfp_mask & __GFP_FS) && mapping)
- goto isolate_fail;
-
- /*
* Be careful not to clear PageLRU until after we're
* sure the page is not being freed elsewhere -- the
* page release code relies on it.
@@ -1016,6 +1000,22 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
if (unlikely(!get_page_unless_zero(page)))
goto isolate_fail;
+ /*
+ * Migration will fail if an anonymous page is pinned in memory,
+ * so avoid taking lru_lock and isolating it unnecessarily in an
+ * admittedly racy check.
+ */
+ mapping = page_mapping(page);
+ if (!mapping && (page_count(page) - 1) > total_mapcount(page))
+ goto isolate_fail_put;
+
+ /*
+ * Only allow to migrate anonymous pages in GFP_NOFS context
+ * because those do not depend on fs locks.
+ */
+ if (!(cc->gfp_mask & __GFP_FS) && mapping)
+ goto isolate_fail_put;
+
/* Only take pages on LRU: a check now makes later tests safe */
if (!PageLRU(page))
goto isolate_fail_put;