linux-kernel - [PATCH mmotm] radix-tree: rewrite radix_tree_locate

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Message-ID: <alpine.LSU.2.11.1605012108490.1166@eggly.anvils>
Date:	Sun, 1 May 2016 21:13:18 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Matthew Wilcox <willy@...ux.intel.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH mmotm] radix-tree: rewrite radix_tree_locate_item fix

radix_tree_locate_item() is often returning the wrong index, causing
swapoff of shmem to hang because it cannot find the swap entry there.
__locate()'s use of base is bogus, it adds an offset twice into index.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
Fix to radix-tree-rewrite-radix_tree_locate_item.patch

 lib/radix-tree.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- 4.6-rc5-mm1/lib/radix-tree.c	2016-04-30 22:55:06.067184898 -0700
+++ linux/lib/radix-tree.c	2016-05-01 18:52:06.668085420 -0700
@@ -1254,15 +1254,14 @@ struct locate_info {
 static unsigned long __locate(struct radix_tree_node *slot, void *item,
 			      unsigned long index, struct locate_info *info)
 {
-	unsigned long base, i;
+	unsigned long i;
 
 	do {
 		unsigned int shift = slot->shift;
-		base = index & ~((1UL << shift) - 1);
 
 		for (i = (index >> shift) & RADIX_TREE_MAP_MASK;
 		     i < RADIX_TREE_MAP_SIZE;
-		     i++, index = base + (i << shift)) {
+		     i++, index += (1UL << shift)) {
 			struct radix_tree_node *node =
 					rcu_dereference_raw(slot->slots[i]);
 			if (node == RADIX_TREE_RETRY)