[PATCH v3 4/9] PM / QoS: Decouple request alloc from dev_pm_qos_mtx

[Rob Clark <robdclark@gmail.com>]

From: Rob Clark <robdclark@chromium.org>

Similar to the previous patch, move the allocation out from under
dev_pm_qos_mtx, by speculatively doing the allocation and handle
any race after acquiring dev_pm_qos_mtx by freeing the redundant
allocation.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/base/power/qos.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
index f3e0c6b65635..4537d93ddb45 100644
--- a/drivers/base/power/qos.c
+++ b/drivers/base/power/qos.c
@@ -922,17 +922,19 @@ s32 dev_pm_qos_get_user_latency_tolerance(struct device *dev)
  */
 int dev_pm_qos_update_user_latency_tolerance(struct device *dev, s32 val)
 {
+	struct dev_pm_qos_request *req = NULL;
 	int ret;
 
 	ret = dev_pm_qos_constraints_ensure_allocated(dev);
 	if (ret)
 		return ret;
 
+	if (!dev->power.qos->latency_tolerance_req)
+		req = kzalloc(sizeof(*req), GFP_KERNEL);
+
 	mutex_lock(&dev_pm_qos_mtx);
 
 	if (!dev->power.qos->latency_tolerance_req) {
-		struct dev_pm_qos_request *req;
-
 		if (val < 0) {
 			if (val == PM_QOS_LATENCY_TOLERANCE_NO_CONSTRAINT)
 				ret = 0;
@@ -940,7 +942,6 @@ int dev_pm_qos_update_user_latency_tolerance(struct device *dev, s32 val)
 				ret = -EINVAL;
 			goto out;
 		}
-		req = kzalloc(sizeof(*req), GFP_KERNEL);
 		if (!req) {
 			ret = -ENOMEM;
 			goto out;
@@ -952,6 +953,13 @@ int dev_pm_qos_update_user_latency_tolerance(struct device *dev, s32 val)
 		}
 		dev->power.qos->latency_tolerance_req = req;
 	} else {
+		/*
+		 * If we raced with another thread to allocate the request,
+		 * simply free the redundant allocation and move on.
+		 */
+		if (req)
+			kfree(req);
+
 		if (val < 0) {
 			__dev_pm_qos_drop_user_request(dev, DEV_PM_QOS_LATENCY_TOLERANCE);
 			ret = 0;
-- 
2.41.0