6.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
commit cbc02854331edc6dc22d8b77b6e22e38ebc7dd51 upstream.
It is possible for xa_load() to observe a sibling entry pointing to
another sibling entry. An example:
Thread A: Thread B:
xa_store_range(xa, entry, 188, 191, gfp);
xa_load(xa, 191);
entry = xa_entry(xa, node, 63);
[entry is a sibling of 188]
xa_store_range(xa, entry, 184, 191, gfp);
if (xa_is_sibling(entry))
offset = xa_to_sibling(entry);
entry = xa_entry(xas->xa, node, offset);
[entry is now a sibling of 184]
It is sufficient to go around this loop until we hit a non-sibling entry.
Sibling entries always point earlier in the node, so we are guaranteed
to terminate this search.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
lib/xarray.c | 2 -
tools/testing/radix-tree/multiorder.c | 68 +++++++++++++++++++++++++++++++++-
2 files changed, 67 insertions(+), 3 deletions(-)
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -206,7 +206,7 @@ static void *xas_descend(struct xa_state
void *entry = xa_entry(xas->xa, node, offset);
xas->xa_node = node;
- if (xa_is_sibling(entry)) {
+ while (xa_is_sibling(entry)) {
offset = xa_to_sibling(entry);
entry = xa_entry(xas->xa, node, offset);
if (node->shift && xa_is_node(entry))
--- a/tools/testing/radix-tree/multiorder.c
+++ b/tools/testing/radix-tree/multiorder.c
@@ -159,7 +159,7 @@ void multiorder_tagged_iteration(struct
item_kill_tree(xa);
}
-bool stop_iteration = false;
+bool stop_iteration;
static void *creator_func(void *ptr)
{
@@ -201,6 +201,7 @@ static void multiorder_iteration_race(st
pthread_t worker_thread[num_threads];
int i;
+ stop_iteration = false;
pthread_create(&worker_thread[0], NULL, &creator_func, xa);
for (i = 1; i < num_threads; i++)
pthread_create(&worker_thread[i], NULL, &iterator_func, xa);
@@ -211,6 +212,61 @@ static void multiorder_iteration_race(st
item_kill_tree(xa);
}
+static void *load_creator(void *ptr)
+{
+ /* 'order' is set up to ensure we have sibling entries */
+ unsigned int order;
+ struct radix_tree_root *tree = ptr;
+ int i;
+
+ rcu_register_thread();
+ item_insert_order(tree, 3 << RADIX_TREE_MAP_SHIFT, 0);
+ item_insert_order(tree, 2 << RADIX_TREE_MAP_SHIFT, 0);
+ for (i = 0; i < 10000; i++) {
+ for (order = 1; order < RADIX_TREE_MAP_SHIFT; order++) {
+ unsigned long index = (3 << RADIX_TREE_MAP_SHIFT) -
+ (1 << order);
+ item_insert_order(tree, index, order);
+ item_delete_rcu(tree, index);
+ }
+ }
+ rcu_unregister_thread();
+
+ stop_iteration = true;
+ return NULL;
+}
+
+static void *load_worker(void *ptr)
+{
+ unsigned long index = (3 << RADIX_TREE_MAP_SHIFT) - 1;
+
+ rcu_register_thread();
+ while (!stop_iteration) {
+ struct item *item = xa_load(ptr, index);
+ assert(!xa_is_internal(item));
+ }
+ rcu_unregister_thread();
+
+ return NULL;
+}
+
+static void load_race(struct xarray *xa)
+{
+ const int num_threads = sysconf(_SC_NPROCESSORS_ONLN) * 4;
+ pthread_t worker_thread[num_threads];
+ int i;
+
+ stop_iteration = false;
+ pthread_create(&worker_thread[0], NULL, &load_creator, xa);
+ for (i = 1; i < num_threads; i++)
+ pthread_create(&worker_thread[i], NULL, &load_worker, xa);
+
+ for (i = 0; i < num_threads; i++)
+ pthread_join(worker_thread[i], NULL);
+
+ item_kill_tree(xa);
+}
+
static DEFINE_XARRAY(array);
void multiorder_checks(void)
@@ -218,12 +274,20 @@ void multiorder_checks(void)
multiorder_iteration(&array);
multiorder_tagged_iteration(&array);
multiorder_iteration_race(&array);
+ load_race(&array);
radix_tree_cpu_dead(0);
}
-int __weak main(void)
+int __weak main(int argc, char **argv)
{
+ int opt;
+
+ while ((opt = getopt(argc, argv, "ls:v")) != -1) {
+ if (opt == 'v')
+ test_verbose++;
+ }
+
rcu_register_thread();
radix_tree_init();
multiorder_checks();
