mm: release private data before split THP

If there is private data attached to a THP, the refcount of THP will be
increased and will prevent the THP from being split.  Attempt to release
any private data attached to the THP before attempting the split to
increase the chance of splitting successfully.

There was a memory failure issue hit during HW error injection testing
with 5.18 kernel + xfs as rootfs.  The test was killed and a system reboot
was required to re-run the test.

The issue was tracked down to a THP split failure caused by the memory
failure not being handled.  The page dump showed:

[ 1785.433075] page:0000000025f9530b refcount:18 mapcount:0 mapping:000000008162eea7 index:0xa10 pfn:0x2f0200
[ 1785.443954] head:0000000025f9530b order:4 compound_mapcount:0 compound_pincount:0
[ 1785.452408] memcg:ff4247f2d28e9000
[ 1785.456304] aops:xfs_address_space_operations ino:8555182 dentry name:"baseos-filenames.solvx"
[ 1785.466612] flags: 0x1000000000012036(referenced|uptodate|lru|active|private|head|node=0|zone=2)
[ 1785.476514] raw: 1000000000012036 ffb9460f8bc07c08 ffb9460f8bc08408 ff4247f22e6299f8
[ 1785.485268] raw: 0000000000000a10 ff4247f194ade900 00000012ffffffff ff4247f2d28e9000

It was like the error was injected to a large folio for xfs with private
data attached.

With private data released before splitting the THP, the test case could
be run successfully many times without rebooting the system.

Link: https://lkml.kernel.org/r/20220810064907.582899-1-fengwei.yin@intel.comCo-developed-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/huge_memory.c

@@ -2643,6 +2643,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 		mapping = NULL;
 		anon_vma_lock_write(anon_vma);
 	} else {
+		gfp_t gfp;
+
 		mapping = head->mapping;
 
 		/* Truncated ? */
@@ -2651,8 +2653,16 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 			goto out;
 		}
 
-		xas_split_alloc(&xas, head, compound_order(head),
-				mapping_gfp_mask(mapping) & GFP_RECLAIM_MASK);
+		gfp = current_gfp_context(mapping_gfp_mask(mapping) &
+							GFP_RECLAIM_MASK);
+
+		if (folio_test_private(folio) &&
+				!filemap_release_folio(folio, gfp)) {
+			ret = -EBUSY;
+			goto out;
+		}
+
+		xas_split_alloc(&xas, head, compound_order(head), gfp);
 		if (xas_error(&xas)) {
 			ret = xas_error(&xas);
 			goto out;