linux-kernel - [PATCH v2 18/23] PM / QoS: Decouple request alloc from dev_pm_qos

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Date:   Mon, 20 Mar 2023 07:43:40 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Daniel Vetter <daniel@...ll.ch>, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, Rob Clark <robdclark@...omium.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pm@...r.kernel.org (open list:POWER MANAGEMENT CORE),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2 18/23] PM / QoS: Decouple request alloc from dev_pm_qos_mtx

From: Rob Clark <robdclark@...omium.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@...omium.org>
---
 drivers/base/power/qos.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
index f3e0c6b65635..9cba334b3729 100644
--- a/drivers/base/power/qos.c
+++ b/drivers/base/power/qos.c
@@ -922,12 +922,16 @@ 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) {
@@ -940,7 +944,6 @@ 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 +955,13 @@ 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;
-- 
2.39.2