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authorMatthew Wilcox <willy@linux.intel.com>2016-02-02 16:57:52 -0800
committerJiri Slaby <jslaby@suse.cz>2016-02-25 10:49:15 +0100
commit44e026574e970b19ce548b659459ed8286cc5a44 (patch)
treeb7bc3a2877c171e55a3d3cada46b1e995c4f2617
parent1c2456e301b60e027413bc4aec797a343a2b0d50 (diff)
radix-tree: fix race in gang lookup
commit 46437f9a554fbe3e110580ca08ab703b59f2f95a upstream. 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
-rw-r--r--include/linux/radix-tree.h16
-rw-r--r--lib/radix-tree.c12
2 files changed, 26 insertions, 2 deletions
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index e8be53ecfc45..3c2ce3cdd16a 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -320,6 +320,22 @@ 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
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index e8adb5d8a184..50a9a1c155d3 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -977,9 +977,13 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
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;
}
@@ -1056,9 +1060,13 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
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;
}