linux-kernel - [PATCH v2 16/23] PM / devfreq: Teach lockdep about locking order

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Date:   Mon, 20 Mar 2023 07:43:38 -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>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        linux-pm@...r.kernel.org (open list:DEVICE FREQUENCY (DEVFREQ)),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2 16/23] PM / devfreq: Teach lockdep about locking order

From: Rob Clark <robdclark@...omium.org>

This will make it easier to catch places doing allocations that can
trigger reclaim under devfreq->lock.

Because devfreq->lock is held over various devfreq_dev_profile
callbacks, there might be some fallout if those callbacks do allocations
that can trigger reclaim, but I've looked through the various callback
implementations and don't see anything obvious.  If it does trigger any
lockdep splats, those should be fixed.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/devfreq/devfreq.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 11b774048bd2..5ce3bf9b59e7 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -817,6 +817,12 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	}
 
 	mutex_init(&devfreq->lock);
+
+	/* Teach lockdep about lock ordering wrt. shrinker: */
+	fs_reclaim_acquire(GFP_KERNEL);
+	might_lock(&devfreq->lock);
+	fs_reclaim_release(GFP_KERNEL);
+
 	devfreq->dev.parent = dev;
 	devfreq->dev.class = devfreq_class;
 	devfreq->dev.release = devfreq_dev_release;
-- 
2.39.2