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XArray: Do not return sibling entries from xa_load()

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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@infradead.org>
Fixes: 6b24ca4a1a ("mm: Use multi-index entries in the page cache")
Cc: stable@vger.kernel.org
This commit is contained in:
Matthew Wilcox (Oracle) 2023-07-26 22:58:17 -04:00
parent f837f0a3c9
commit cbc0285433
2 changed files with 67 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
lib/xarray.c
View File

@ -206,7 +206,7 @@ static void *xas_descend(struct xa_state *xas, struct xa_node *node)
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))

68
tools/testing/radix-tree/multiorder.c
View File

@ -159,7 +159,7 @@ void multiorder_tagged_iteration(struct xarray *xa)
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(struct xarray *xa)
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(struct xarray *xa)
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();