[PATCH v2 05/12] platform/x86: lenovo-wmi-capdata: Defer mutex initialization

[Rong Zhang]

In the following changes, priv->list may be freed if the first call to
lwmi_cd_cache() fails due to WMI/ACPI errors, so the list_mutex must be
initialized after it in order not to break lockdep, as there is no
devm_mutex_destroy(). Considering that the first call to lwmi_cd_cache()
doesn't need serialization as there is no other reader or writer this
early, the initialization of list_mutex can be deferred.

Therefore, initialize list_mutex only after the first call to
lwmi_cd_cache() succeeds, otherwise it remains uninitialized and can be
devm_kfree()-ed.

Signed-off-by: Rong Zhang <i@xxxxxxxx>
---
Changes in v2:
- Synchronize the initialization with release-acquire barriers (thanks
  Ilpo Järvinen)
---
 drivers/platform/x86/lenovo/wmi-capdata.c | 86 +++++++++++++++++++++++--------
 1 file changed, 65 insertions(+), 21 deletions(-)

diff --git a/drivers/platform/x86/lenovo/wmi-capdata.c b/drivers/platform/x86/lenovo/wmi-capdata.c
index 3008d6d699c0..e52cb2de49a6 100644
--- a/drivers/platform/x86/lenovo/wmi-capdata.c
+++ b/drivers/platform/x86/lenovo/wmi-capdata.c
@@ -48,6 +48,8 @@
 #include <linux/types.h>
 #include <linux/wmi.h>
 
+#include <asm/barrier.h>
+
 #include "wmi-capdata.h"
 #include "wmi-helpers.h"
 
@@ -91,6 +93,7 @@ struct lwmi_cd_priv {
 	struct wmi_device *wdev;
 	struct cd_list *list;
 	struct dentry *debugfs_dir;
+	bool initialized;
 
 	/*
 	 * A capdata device may be a component master of another capdata device.
@@ -588,14 +591,14 @@ static void lwmi_cd_debugfs_remove(struct lwmi_cd_priv *priv)
 /* ======== WMI interface ======== */
 
 /**
- * lwmi_cd_cache() - Cache all WMI data block information
+ * __lwmi_cd_cache() - Cache all WMI data block information locklessly
  * @priv: lenovo-wmi-capdata driver data.
  *
- * Loop through each WMI data block and cache the data.
+ * Loop through each WMI data block and cache the data locklessly.
  *
  * Return: 0 on success, or an error.
  */
-static int lwmi_cd_cache(struct lwmi_cd_priv *priv)
+static int __lwmi_cd_cache(struct lwmi_cd_priv *priv)
 {
 	size_t size;
 	int idx;
@@ -617,7 +620,6 @@ static int lwmi_cd_cache(struct lwmi_cd_priv *priv)
 		return -EINVAL;
 	}
 
-	guard(mutex)(&priv->list->list_mutex);
 	for (idx = 0; idx < priv->list->count; idx++, p += size) {
 		union acpi_object *ret_obj __free(kfree) = NULL;
 
@@ -635,14 +637,38 @@ static int lwmi_cd_cache(struct lwmi_cd_priv *priv)
 	return 0;
 }
 
+/**
+ * lwmi_cd_cache() - Cache all WMI data block information
+ * @priv: lenovo-wmi-capdata driver data.
+ *
+ * Loop through each WMI data block and cache the data.
+ *
+ * Return: 0 on success, or an error.
+ */
+static int lwmi_cd_cache(struct lwmi_cd_priv *priv)
+{
+	/* Synchronize mutex initialization. Paired with lwmi_cd_finalize(). */
+	if (!smp_load_acquire(&priv->initialized))
+		return __lwmi_cd_cache(priv);
+
+	switch (priv->info->type) {
+	case LENOVO_CAPABILITY_DATA_01:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	guard(mutex)(&priv->list->list_mutex);
+	return __lwmi_cd_cache(priv);
+}
+
 /**
  * lwmi_cd_fan_list_alloc_cache() - Alloc and cache Fan Test Data list
  * @priv: lenovo-wmi-capdata driver data.
- * @listptr: Pointer to returned cd_list pointer.
  *
- * Return: count of fans found, or an error.
+ * Return: 0 on success, or an error.
  */
-static int lwmi_cd_fan_list_alloc_cache(struct lwmi_cd_priv *priv, struct cd_list **listptr)
+static int lwmi_cd_fan_list_alloc_cache(struct lwmi_cd_priv *priv)
 {
 	struct cd_list *list;
 	size_t size;
@@ -688,6 +714,9 @@ static int lwmi_cd_fan_list_alloc_cache(struct lwmi_cd_priv *priv, struct cd_lis
 	if (!list)
 		return -ENOMEM;
 
+	list->count = count;
+	priv->list = list;
+
 	for (idx = 0; idx < count; idx++) {
 		/* Do not calculate array index using count, as it may be truncated. */
 		list->cd_fan[idx] = (struct capdata_fan) {
@@ -697,8 +726,7 @@ static int lwmi_cd_fan_list_alloc_cache(struct lwmi_cd_priv *priv, struct cd_lis
 		};
 	}
 
-	*listptr = list;
-	return count;
+	return 0;
 }
 
 /**
@@ -714,7 +742,7 @@ static int lwmi_cd_alloc(struct lwmi_cd_priv *priv)
 {
 	struct cd_list *list;
 	size_t list_size;
-	int count, ret;
+	int count;
 
 	count = wmidev_instance_count(priv->wdev);
 
@@ -726,11 +754,7 @@ static int lwmi_cd_alloc(struct lwmi_cd_priv *priv)
 		list_size = struct_size(list, cd01, count);
 		break;
 	case LENOVO_FAN_TEST_DATA:
-		count = lwmi_cd_fan_list_alloc_cache(priv, &list);
-		if (count < 0)
-			return count;
-
-		goto got_list;
+		return lwmi_cd_fan_list_alloc_cache(priv);
 	default:
 		return -EINVAL;
 	}
@@ -739,17 +763,33 @@ static int lwmi_cd_alloc(struct lwmi_cd_priv *priv)
 	if (!list)
 		return -ENOMEM;
 
-got_list:
-	ret = devm_mutex_init(&priv->wdev->dev, &list->list_mutex);
-	if (ret)
-		return ret;
-
 	list->count = count;
 	priv->list = list;
 
 	return 0;
 }
 
+/**
+ * lwmi_cd_finalize() - Finalize the capability data initialization
+ * @priv: lenovo-wmi-capdata driver data.
+ *
+ * Return: 0 on success, or an error code.
+ */
+static int lwmi_cd_finalize(struct lwmi_cd_priv *priv)
+{
+	int ret;
+
+	if (priv->list) {
+		ret = devm_mutex_init(&priv->wdev->dev, &priv->list->list_mutex);
+		if (ret)
+			return ret;
+	}
+
+	/* Synchronize mutex initialization. Paired with lwmi_cd_cache(). */
+	smp_store_release(&priv->initialized, 1);
+	return 0;
+}
+
 /**
  * lwmi_cd_setup() - Cache all WMI data block information
  * @priv: lenovo-wmi-capdata driver data.
@@ -768,7 +808,11 @@ static int lwmi_cd_setup(struct lwmi_cd_priv *priv)
 	if (ret)
 		return ret;
 
-	return lwmi_cd_cache(priv);
+	ret = lwmi_cd_cache(priv);
+	if (ret)
+		return ret;
+
+	return lwmi_cd_finalize(priv);
 }
 
 /**

-- 
2.55.0