[PW_SID:1066741] [bpf,v2] bpf: do not use kmalloc_nolock when !HAVE_CMPXCHG_DOUBLE

include/linux/bpf_local_storage.h

@@ -19,6 +19,8 @@
 
 #define BPF_LOCAL_STORAGE_CACHE_SIZE	16
 
+static const bool KMALLOC_NOLOCK_SUPPORTED = IS_ENABLED(CONFIG_HAVE_CMPXCHG_DOUBLE);
+
 struct bpf_local_storage_map_bucket {
 	struct hlist_head list;
 	rqspinlock_t lock;

kernel/bpf/bpf_cgrp_storage.c

@@ -114,7 +114,7 @@ static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
 
 static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
 {
-	return bpf_local_storage_map_alloc(attr, &cgroup_cache, true);
+	return bpf_local_storage_map_alloc(attr, &cgroup_cache, KMALLOC_NOLOCK_SUPPORTED);
 }
 
 static void cgroup_storage_map_free(struct bpf_map *map)

kernel/bpf/bpf_local_storage.c

@@ -889,6 +889,10 @@ bpf_local_storage_map_alloc(union bpf_attr *attr,
 	/* In PREEMPT_RT, kmalloc(GFP_ATOMIC) is still not safe in non
 	 * preemptible context. Thus, enforce all storages to use
 	 * kmalloc_nolock() when CONFIG_PREEMPT_RT is enabled.
+	 *
+	 * However, kmalloc_nolock would fail on architectures that do not
+	 * have CMPXCHG_DOUBLE. On such architectures with PREEMPT_RT,
+	 * bpf_local_storage_alloc would always fail.
 	 */
 	smap->use_kmalloc_nolock = IS_ENABLED(CONFIG_PREEMPT_RT) ? true : use_kmalloc_nolock;
 

kernel/bpf/bpf_task_storage.c

@@ -212,7 +212,7 @@ static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
 
 static struct bpf_map *task_storage_map_alloc(union bpf_attr *attr)
 {
-	return bpf_local_storage_map_alloc(attr, &task_cache, true);
+	return bpf_local_storage_map_alloc(attr, &task_cache, KMALLOC_NOLOCK_SUPPORTED);
 }
 
 static void task_storage_map_free(struct bpf_map *map)