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authorMatthew Wilcox <willy@linux.intel.com>2016-02-02 16:57:52 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-02-03 08:28:43 -0800
commit46437f9a554fbe3e110580ca08ab703b59f2f95a (patch)
tree826c5a8180792c3c68f57686d41bf69f01b2985d /include
parent3c1da7beeee02560cd0f0c66c5a59fce3c6746e3 (diff)
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@linux.intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Ohad Ben-Cohen <ohad@wizery.com> Cc: Konstantin Khlebnikov <khlebnikov@openvz.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/radix-tree.h16
1 files changed, 16 insertions, 0 deletions
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 7c88ad156a29..00b17c526c1f 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -379,6 +379,22 @@ void **radix_tree_next_chunk(struct radix_tree_root *root,
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