bpf: Refactor the core bpf_task_storage_get logic into a new function

This patch creates a new function __bpf_task_storage_get() and
moves the core logic of the existing bpf_task_storage_get()
into this new function.   This new function will be shared
by another new helper proto in the latter patch.
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20221025184524.3526117-4-martin.lau@linux.devSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/bpf_task_storage.c

@@ -227,37 +227,45 @@ static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
 	return err;
 }
 
-/* *gfp_flags* is a hidden argument provided by the verifier */
-BPF_CALL_5(bpf_task_storage_get_recur, struct bpf_map *, map, struct task_struct *,
-	   task, void *, value, u64, flags, gfp_t, gfp_flags)
+/* Called by bpf_task_storage_get*() helpers */
+static void *__bpf_task_storage_get(struct bpf_map *map,
+				    struct task_struct *task, void *value,
+				    u64 flags, gfp_t gfp_flags)
 {
 	struct bpf_local_storage_data *sdata;
 
-	WARN_ON_ONCE(!bpf_rcu_lock_held());
-	if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
-		return (unsigned long)NULL;
-
-	if (!task)
-		return (unsigned long)NULL;
-
-	if (!bpf_task_storage_trylock())
-		return (unsigned long)NULL;
-
 	sdata = task_storage_lookup(task, map, true);
 	if (sdata)
-		goto unlock;
+		return sdata->data;
 
 	/* only allocate new storage, when the task is refcounted */
 	if (refcount_read(&task->usage) &&
-	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
+	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE)) {
 		sdata = bpf_local_storage_update(
 			task, (struct bpf_local_storage_map *)map, value,
 			BPF_NOEXIST, gfp_flags);
+		return IS_ERR(sdata) ? NULL : sdata->data;
+	}
 
-unlock:
+	return NULL;
+}
+
+/* *gfp_flags* is a hidden argument provided by the verifier */
+BPF_CALL_5(bpf_task_storage_get_recur, struct bpf_map *, map, struct task_struct *,
+	   task, void *, value, u64, flags, gfp_t, gfp_flags)
+{
+	void *data;
+
+	WARN_ON_ONCE(!bpf_rcu_lock_held());
+	if (flags & ~BPF_LOCAL_STORAGE_GET_F_CREATE || !task)
+		return (unsigned long)NULL;
+
+	if (!bpf_task_storage_trylock())
+		return (unsigned long)NULL;
+	data = __bpf_task_storage_get(map, task, value, flags,
+				      gfp_flags);
 	bpf_task_storage_unlock();
-	return IS_ERR_OR_NULL(sdata) ? (unsigned long)NULL :
-		(unsigned long)sdata->data;
+	return (unsigned long)data;
 }
 
 BPF_CALL_2(bpf_task_storage_delete_recur, struct bpf_map *, map, struct task_struct *,