The patch titled
Subject: radix-tree: fix race in gang lookup
has been added to the -mm tree. Its filename is
radix-tree-fix-race-in-gang-lookup.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/radix-tree-fix-race-in-gang-lookup.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/radix-tree-fix-race-in-gang-lookup.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Subject: radix-tree: fix race in gang lookup
If the indirect_ptr bit is set on a slot, that indicates we need to redo
the lookup. Introduce a new function radix_tree_iter_retry() which forces
the loop to retry the lookup by setting 'slot' to NULL and turning the
iterator back to point at the problematic entry.
This is a pretty rare problem to hit at the moment; the lookup has to race
with a grow of the radix tree from a height of 0. The consequences of
hitting this race are that gang lookup could return a pointer to a
radix_tree_node instead of a pointer to whatever the user had inserted in
the tree.
Fixes: cebbd29e1c2f ("radix-tree: rewrite gang lookup using iterator")
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Ohad Ben-Cohen <ohad@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/radix-tree.h | 16 ++++++++++++++++
lib/radix-tree.c | 12 ++++++++++--
2 files changed, 26 insertions(+), 2 deletions(-)
diff -puN include/linux/radix-tree.h~radix-tree-fix-race-in-gang-lookup include/linux/radix-tree.h
--- a/include/linux/radix-tree.h~radix-tree-fix-race-in-gang-lookup
+++ a/include/linux/radix-tree.h
@@ -379,6 +379,22 @@ void **radix_tree_next_chunk(struct radi
struct radix_tree_iter *iter, unsigned flags);
/**
+ * radix_tree_iter_retry - retry this chunk of the iteration
+ * @iter: iterator state
+ *
+ * If we iterate over a tree protected only by the RCU lock, a race
+ * against deletion or creation may result in seeing a slot for which
+ * radix_tree_deref_retry() returns true. If so, call this function
+ * and continue the iteration.
+ */
+static inline __must_check
+void **radix_tree_iter_retry(struct radix_tree_iter *iter)
+{
+ iter->next_index = iter->index;
+ return NULL;
+}
+
+/**
* radix_tree_chunk_size - get current chunk size
*
* @iter: pointer to radix tree iterator
diff -puN lib/radix-tree.c~radix-tree-fix-race-in-gang-lookup lib/radix-tree.c
--- a/lib/radix-tree.c~radix-tree-fix-race-in-gang-lookup
+++ a/lib/radix-tree.c
@@ -1019,9 +1019,13 @@ radix_tree_gang_lookup(struct radix_tree
return 0;
radix_tree_for_each_slot(slot, root, &iter, first_index) {
- results[ret] = indirect_to_ptr(rcu_dereference_raw(*slot));
+ results[ret] = rcu_dereference_raw(*slot);
if (!results[ret])
continue;
+ if (radix_tree_is_indirect_ptr(results[ret])) {
+ slot = radix_tree_iter_retry(&iter);
+ continue;
+ }
if (++ret == max_items)
break;
}
@@ -1098,9 +1102,13 @@ radix_tree_gang_lookup_tag(struct radix_
return 0;
radix_tree_for_each_tagged(slot, root, &iter, first_index, tag) {
- results[ret] = indirect_to_ptr(rcu_dereference_raw(*slot));
+ results[ret] = rcu_dereference_raw(*slot);
if (!results[ret])
continue;
+ if (radix_tree_is_indirect_ptr(results[ret])) {
+ slot = radix_tree_iter_retry(&iter);
+ continue;
+ }
if (++ret == max_items)
break;
}
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxxxx are
radix-tree-fix-race-in-gang-lookup.patch
hwspinlock-fix-race-between-radix-tree-insertion-and-lookup.patch
radix-tree-add-an-explicit-include-of-bitopsh.patch
radix-tree-test-harness.patch
radix_tree-tag-all-internal-tree-nodes-as-indirect-pointers.patch
radix_tree-loop-based-on-shift-count-not-height.patch
radix_tree-add-support-for-multi-order-entries.patch
radix_tree-add-radix_tree_dump.patch
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