linux-kernel - [PATCH 5.16 0926/1017] XArray: Update the LRU list in xas

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Message-Id: <20220405070421.703881433@linuxfoundation.org>
Date:   Tue,  5 Apr 2022 09:30:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: [PATCH 5.16 0926/1017] XArray: Update the LRU list in xas_split()

From: Matthew Wilcox (Oracle) <willy@...radead.org>

commit 3ed4bb77156da0bc732847c8c9df92454c1fbeea upstream.

When splitting a value entry, we may need to add the new nodes to the LRU
list and remove the parent node from the LRU list.  The WARN_ON checks
in shadow_lru_isolate() catch this oversight.  This bug was latent
until we stopped splitting folios in shrink_page_list() with commit
820c4e2e6f51 ("mm/vmscan: Free non-shmem folios without splitting them").
That allows the creation of large shadow entries, and subsequently when
trying to page in a small page, we will split the large shadow entry
in __filemap_add_folio().

Fixes: 8fc75643c5e1 ("XArray: add xas_split")
Reported-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 lib/xarray.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1081,6 +1081,7 @@ void xas_split(struct xa_state *xas, voi
 					xa_mk_node(child));
 			if (xa_is_value(curr))
 				values--;
+			xas_update(xas, child);
 		} else {
 			unsigned int canon = offset - xas->xa_sibs;
 
@@ -1095,6 +1096,7 @@ void xas_split(struct xa_state *xas, voi
 	} while (offset-- > xas->xa_offset);
 
 	node->nr_values += values;
+	xas_update(xas, node);
 }
 EXPORT_SYMBOL_GPL(xas_split);
 #endif