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[PATCH v3 15/33] radix-tree: Move rcu_head into a union with private_list

From Matthew Wilcox <mawilcox@linuxonhyperv.com>
Newsgroups linux.kernel
Subject [PATCH v3 15/33] radix-tree: Move rcu_head into a union with private_list
Date 2016-11-28 21:10 +0100
Message-ID <sIApt-6LC-71@gated-at.bofh.it> (permalink)
References <sIAfL-6sT-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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From: Matthew Wilcox <willy@infradead.org>

I want to be able to reference node->parent after freeing node.
Currently node->parent is in a union with rcu_head, so it is overwritten
when the node is put on the RCU list.  We know that private_list is not
referenced after the node is freed, so it is safe for these two members
to share space.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
---
 include/linux/radix-tree.h | 14 ++++----------
 lib/radix-tree.c           |  1 +
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 7444860..d04073a 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -85,18 +85,12 @@ struct radix_tree_node {
 	unsigned char	offset;		/* Slot offset in parent */
 	unsigned char	count;		/* Total entry count */
 	unsigned char	exceptional;	/* Exceptional entry count */
+	struct radix_tree_node *parent;		/* Used when ascending tree */
+	void *private_data;			/* For tree user */
 	union {
-		struct {
-			/* Used when ascending tree */
-			struct radix_tree_node *parent;
-			/* For tree user */
-			void *private_data;
-		};
-		/* Used when freeing node */
-		struct rcu_head	rcu_head;
+		struct list_head private_list;	/* For tree user */
+		struct rcu_head	rcu_head;	/* Used when freeing node */
 	};
-	/* For tree user */
-	struct list_head private_list;
 	void __rcu	*slots[RADIX_TREE_MAP_SIZE];
 	unsigned long	tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
 };
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index b329056..3f49417 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -324,6 +324,7 @@ static void radix_tree_node_rcu_free(struct rcu_head *head)
 		tag_clear(node, i, 0);
 
 	node->slots[0] = NULL;
+	INIT_LIST_HEAD(&node->private_list);
 
 	kmem_cache_free(radix_tree_node_cachep, node);
 }
-- 
2.10.2

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[PATCH v3 00/33] Radix tree patches for 4.10 Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 26/33] radix-tree: Fix replacement for multiorder entries Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 00/33] Radix tree patches for 4.10 Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 27/33] radix tree test suite: Check multiorder iteration Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 15/33] radix-tree: Move rcu_head into a union with private_list Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 23/33] radix-tree: Add radix_tree_join Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 09/33] radix tree test suite: Use rcu_barrier Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 16/33] radix-tree: Create node_tag_set() Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 25/33] radix-tree: Add radix_tree_split_preload() Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 09/33] radix tree test suite: Use rcu_barrier Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 12/33] tools: Add more bitmap functions Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 16/33] radix-tree: Create node_tag_set() Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 27/33] radix tree test suite: Check multiorder iteration Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 21/33] radix-tree: Delete radix_tree_locate_item() Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:10 +0100
  [PATCH v3 08/33] radix tree test suite: benchmark for iterator Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 22/33] radix-tree: Delete radix_tree_range_tag_if_tagged() Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 17/33] radix-tree: Make radix_tree_find_next_bit more useful Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 23/33] radix-tree: Add radix_tree_join Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 18/33] radix-tree: Improve dump output Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 05/33] radix tree test suite: Free preallocated nodes Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 06/33] radix tree test suite: Make runs more reproducible Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 20/33] radix-tree: Improve multiorder iterators Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 02/33] tools: Add WARN_ON_ONCE Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 14/33] radix-tree: Fix typo Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 03/33] radix tree test suite: Allow GFP_ATOMIC allocations to fail Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 12/33] tools: Add more bitmap functions Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 10/33] radix tree test suite: Handle exceptional entries Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 24/33] radix-tree: Add radix_tree_split Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
    Re: [PATCH v3 24/33] radix-tree: Add radix_tree_split Randy Dunlap <rdunlap@infradead.org> - 2016-11-29 01:10 +0100
      RE: [PATCH v3 24/33] radix-tree: Add radix_tree_split Matthew Wilcox <mawilcox@microsoft.com> - 2016-11-29 16:00 +0100
  [PATCH v3 15/33] radix-tree: Move rcu_head into a union with private_list Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 11/33] radix tree test suite: record order in each item Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 01/33] radix tree test suite: Fix compilation Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 08/33] radix tree test suite: benchmark for iterator Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 17/33] radix-tree: Make radix_tree_find_next_bit more useful Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  [PATCH v3 10/33] radix tree test suite: Handle exceptional entries Matthew Wilcox <mawilcox@linuxonhyperv.com> - 2016-11-28 21:20 +0100
  Re: [PATCH v3 00/33] Radix tree patches for 4.10 "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-11-29 12:30 +0100
  Re: [PATCH v3 33/33] Reimplement IDR and IDA using the radix tree Andrew Morton <akpm@linux-foundation.org> - 2016-12-06 21:50 +0100
    Re: [PATCH v3 33/33] Reimplement IDR and IDA using the radix tree Andrew Morton <akpm@linux-foundation.org> - 2016-12-06 22:30 +0100
    RE: [PATCH v3 33/33] Reimplement IDR and IDA using the radix tree Matthew Wilcox <mawilcox@microsoft.com> - 2016-12-06 23:00 +0100

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