From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: maarten.lankhorst@linux.intel.com, mripard@kernel.org,
tzimmermann@suse.de, airlied@linux.ie, daniel@ffwll.ch,
sumit.semwal@linaro.org, christian.koenig@amd.com
Cc: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org,
gregkh@linuxfoundation.org,
linux-kernel-mentees@lists.linuxfoundation.org,
emil.l.velikov@gmail.com
Subject: [PATCH v6 2/4] drm: avoid circular locks in __drm_mode_object_find
Date: Wed, 30 Jun 2021 22:54:02 +0800 [thread overview]
Message-ID: <20210630145404.5958-3-desmondcheongzx@gmail.com> (raw)
In-Reply-To: <20210630145404.5958-1-desmondcheongzx@gmail.com>
In a future patch, _drm_lease_held will dereference drm_file->master
only after making a call to drm_file_get_master which increments the
reference count of drm_file->master while holding a lock on
drm_device.master_mutex.
In preparation for this, the call to _drm_lease_held should be moved
out from the section locked by &dev->mode_config.idr_mutex. This
avoids inverting the lock hierarchy for
&dev->master_mutex --> &dev->mode_config.idr_mutex
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---
drivers/gpu/drm/drm_mode_object.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/drm_mode_object.c b/drivers/gpu/drm/drm_mode_object.c
index b26588b52795..63d35f1f98dd 100644
--- a/drivers/gpu/drm/drm_mode_object.c
+++ b/drivers/gpu/drm/drm_mode_object.c
@@ -146,16 +146,18 @@ struct drm_mode_object *__drm_mode_object_find(struct drm_device *dev,
if (obj && obj->id != id)
obj = NULL;
- if (obj && drm_mode_object_lease_required(obj->type) &&
- !_drm_lease_held(file_priv, obj->id))
- obj = NULL;
-
if (obj && obj->free_cb) {
if (!kref_get_unless_zero(&obj->refcount))
obj = NULL;
}
mutex_unlock(&dev->mode_config.idr_mutex);
+ if (obj && drm_mode_object_lease_required(obj->type) &&
+ !_drm_lease_held(file_priv, obj->id)) {
+ drm_mode_object_put(obj);
+ obj = NULL;
+ }
+
return obj;
}
--
2.25.1
next prev parent reply other threads:[~2021-06-30 14:55 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-30 14:54 [PATCH v6 0/4] drm: address potential UAF bugs with drm_master ptrs Desmond Cheong Zhi Xi
2021-06-30 14:54 ` [PATCH v6 1/4] drm: avoid circular locks in drm_mode_getconnector Desmond Cheong Zhi Xi
2021-06-30 14:54 ` Desmond Cheong Zhi Xi [this message]
2021-06-30 14:54 ` [PATCH v6 3/4] drm: add a locked version of drm_is_current_master Desmond Cheong Zhi Xi
2021-06-30 14:54 ` [PATCH v6 4/4] drm: protect drm_master pointers in drm_lease.c Desmond Cheong Zhi Xi
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