linux-kernel - [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm

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Message-Id: <20210818073824.1560124-3-desmondcheongzx@gmail.com>
Date:   Wed, 18 Aug 2021 15:38:17 +0800
From:   Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
To:     maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...ux.ie, daniel@...ll.ch,
        sumit.semwal@...aro.org, christian.koenig@....com, axboe@...nel.dk,
        oleg@...hat.com, tglx@...utronix.de, dvyukov@...gle.com,
        walter-zh.wu@...iatek.com
Cc:     Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, skhan@...uxfoundation.org,
        gregkh@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master

When drm_file.master changes value, the corresponding
drm_device.master_lookup_lock should be held.

In drm_master_release, a call to drm_master_put sets the
file_priv->master to NULL, so we protect this section with
drm_device.master_lookup_lock.

Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
---
 drivers/gpu/drm/drm_auth.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index 8efb58aa7d95..8c0e0dba1611 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -373,8 +373,11 @@ void drm_master_release(struct drm_file *file_priv)
 	}
 
 	/* drop the master reference held by the file priv */
-	if (file_priv->master)
+	if (file_priv->master) {
+		spin_lock(&dev->master_lookup_lock);
 		drm_master_put(&file_priv->master);
+		spin_unlock(&dev->master_lookup_lock);
+	}
 	mutex_unlock(&dev->master_mutex);
 }
 
-- 
2.25.1