maple_tree: add test to replicate low memory race conditions

Add new callback fields to the userspace implementation of struct
kmem_cache.  This allows for executing callback functions in order to
further test low memory scenarios where node allocation is retried.

This callback can help test race conditions by calling a function when a
low memory event is tested.

Link: https://lkml.kernel.org/r/20240812190543.71967-2-sidhartha.kumar@oracle.com
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index b547ff211ac7420ee5db204d914c9da2811d5fe8..14d7864b8d531887591cf39bbf3ba3eacf3c3871 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -7005,6 +7005,19 @@ void mt_set_non_kernel(unsigned int val)
        kmem_cache_set_non_kernel(maple_node_cache, val);
 }
 
+extern void kmem_cache_set_callback(struct kmem_cache *cachep,
+               void (*callback)(void *));
+void mt_set_callback(void (*callback)(void *))
+{
+       kmem_cache_set_callback(maple_node_cache, callback);
+}
+
+extern void kmem_cache_set_private(struct kmem_cache *cachep, void *private);
+void mt_set_private(void *private)
+{
+       kmem_cache_set_private(maple_node_cache, private);
+}
+
 extern unsigned long kmem_cache_get_alloc(struct kmem_cache *);
 unsigned long mt_get_alloc_size(void)
 {

diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
index cd1cf05503b4b4c93a5dedd282583e0c79be91ce..ef5b83cf94eaee70b76e833dc88b5f282d2593ba 100644 (file)
--- a/tools/testing/radix-tree/maple.c
+++ b/tools/testing/radix-tree/maple.c
@@ -36224,6 +36224,65 @@ static noinline void __init check_mtree_dup(struct maple_tree *mt)
 
 extern void test_kmem_cache_bulk(void);
 
+/* callback function used for check_nomem_writer_race() */
+static void writer2(void *maple_tree)
+{
+       struct maple_tree *mt = (struct maple_tree *)maple_tree;
+       MA_STATE(mas, mt, 6, 10);
+
+       mtree_lock(mas.tree);
+       mas_store(&mas, xa_mk_value(0xC));
+       mas_destroy(&mas);
+       mtree_unlock(mas.tree);
+}
+
+/*
+ * check_nomem_writer_race() - test a possible race in the mas_nomem() path
+ * @mt: The tree to build.
+ *
+ * There is a possible race condition in low memory conditions when mas_nomem()
+ * gives up its lock. A second writer can chagne the entry that the primary
+ * writer executing the mas_nomem() path is modifying. This test recreates this
+ * scenario to ensure we are handling it correctly.
+ */
+static void check_nomem_writer_race(struct maple_tree *mt)
+{
+       MA_STATE(mas, mt, 0, 5);
+
+       mt_set_non_kernel(0);
+       /* setup root with 2 values with NULL in between */
+       mtree_store_range(mt, 0, 5, xa_mk_value(0xA), GFP_KERNEL);
+       mtree_store_range(mt, 6, 10, NULL, GFP_KERNEL);
+       mtree_store_range(mt, 11, 15, xa_mk_value(0xB), GFP_KERNEL);
+
+       /* setup writer 2 that will trigger the race condition */
+       mt_set_private(mt);
+       mt_set_callback(writer2);
+
+       mtree_lock(mt);
+       /* erase 0-5 */
+       mas_erase(&mas);
+
+       /* index 6-10 should retain the value from writer 2 */
+       check_load(mt, 6, xa_mk_value(0xC));
+       mtree_unlock(mt);
+
+       /* test for the same race but with mas_store_gfp() */
+       mtree_store_range(mt, 0, 5, xa_mk_value(0xA), GFP_KERNEL);
+       mtree_store_range(mt, 6, 10, NULL, GFP_KERNEL);
+
+       mas_set_range(&mas, 0, 5);
+       mtree_lock(mt);
+       mas_store_gfp(&mas, NULL, GFP_KERNEL);
+
+       /* ensure write made by writer 2 is retained */
+       check_load(mt, 6, xa_mk_value(0xC));
+
+       mt_set_private(NULL);
+       mt_set_callback(NULL);
+       mtree_unlock(mt);
+}
+
 void farmer_tests(void)
 {
        struct maple_node *node;
@@ -36257,6 +36316,10 @@ void farmer_tests(void)
        check_dfs_preorder(&tree);
        mtree_destroy(&tree);
 
+       mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE | MT_FLAGS_USE_RCU);
+       check_nomem_writer_race(&tree);
+       mtree_destroy(&tree);
+
        mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
        check_prealloc(&tree);
        mtree_destroy(&tree);

diff --git a/tools/testing/shared/linux.c b/tools/testing/shared/linux.c
index 4eb442206d019acf29576c3caa4503941f59a229..17263696b5d88040f2901cf367c00677b5c59bfb 100644 (file)
--- a/tools/testing/shared/linux.c
+++ b/tools/testing/shared/linux.c
@@ -26,8 +26,21 @@ struct kmem_cache {
        unsigned int non_kernel;
        unsigned long nr_allocated;
        unsigned long nr_tallocated;
+       bool exec_callback;
+       void (*callback)(void *);
+       void *private;
 };
 
+void kmem_cache_set_callback(struct kmem_cache *cachep, void (*callback)(void *))
+{
+       cachep->callback = callback;
+}
+
+void kmem_cache_set_private(struct kmem_cache *cachep, void *private)
+{
+       cachep->private = private;
+}
+
 void kmem_cache_set_non_kernel(struct kmem_cache *cachep, unsigned int val)
 {
        cachep->non_kernel = val;
@@ -58,9 +71,17 @@ void *kmem_cache_alloc_lru(struct kmem_cache *cachep, struct list_lru *lru,
 {
        void *p;
 
+       if (cachep->exec_callback) {
+               if (cachep->callback)
+                       cachep->callback(cachep->private);
+               cachep->exec_callback = false;
+       }
+
        if (!(gfp & __GFP_DIRECT_RECLAIM)) {
-               if (!cachep->non_kernel)
+               if (!cachep->non_kernel) {
+                       cachep->exec_callback = true;
                        return NULL;
+               }
 
                cachep->non_kernel--;
        }
@@ -223,6 +244,9 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align,
        ret->objs = NULL;
        ret->ctor = ctor;
        ret->non_kernel = 0;
+       ret->exec_callback = false;
+       ret->callback = NULL;
+       ret->private = NULL;
        return ret;
 }