linux-kernel - [PATCH 2/3] drm: clarify lifetime/locking for drm

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Message-Id: <20210722092929.244629-3-desmondcheongzx@gmail.com>
Date:   Thu, 22 Jul 2021 17:29:28 +0800
From:   Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
To:     linux-graphics-maintainer@...are.com, zackr@...are.com,
        airlied@...ux.ie, daniel@...ll.ch,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de
Cc:     Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, skhan@...uxfoundation.org,
        gregkh@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: [PATCH 2/3] drm: clarify lifetime/locking for drm_master's lease fields

In particular, we make it clear that &drm_device.mode_config.idr_mutex
protects the lease idr and list structures for drm_master. The lessor
field itself doesn't need to be protected as it doesn't change after
it's set in drm_lease_create.

Additionally, we add descriptions for the lifetime of lessors and
leases to make it easier to reason about them.

Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
---
 include/drm/drm_auth.h | 62 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 51 insertions(+), 11 deletions(-)

diff --git a/include/drm/drm_auth.h b/include/drm/drm_auth.h
index f99d3417f304..c978c85464fa 100644
--- a/include/drm/drm_auth.h
+++ b/include/drm/drm_auth.h
@@ -58,12 +58,6 @@ struct drm_lock_data {
  * @refcount: Refcount for this master object.
  * @dev: Link back to the DRM device
  * @driver_priv: Pointer to driver-private information.
- * @lessor: Lease holder
- * @lessee_id: id for lessees. Owners always have id 0
- * @lessee_list: other lessees of the same master
- * @lessees: drm_masters leasing from this one
- * @leases: Objects leased to this drm_master.
- * @lessee_idr: All lessees under this owner (only used where lessor == NULL)
  *
  * Note that master structures are only relevant for the legacy/primary device
  * nodes, hence there can only be one per device, not one per drm_minor.
@@ -88,17 +82,63 @@ struct drm_master {
 	struct idr magic_map;
 	void *driver_priv;
 
-	/* Tree of display resource leases, each of which is a drm_master struct
-	 * All of these get activated simultaneously, so drm_device master points
-	 * at the top of the tree (for which lessor is NULL). Protected by
-	 * &drm_device.mode_config.idr_mutex.
+	/**
+	 * @lessor:
+	 *
+	 * Lease holder. The lessor does not change once it's set in
+	 * drm_lease_create(). Each lessee holds a reference to its lessor that
+	 * it releases upon being destroyed in drm_lease_destroy().
+	 *
+	 * Display resource leases form a tree of &struct drm_master. All of
+	 * these get activated simultaneously, so &drm_device.master
+	 * points at the top of the tree (for which lessor is NULL).
 	 */
-
 	struct drm_master *lessor;
+
+	/**
+	 * @lessee_id:
+	 *
+	 * ID for lessees. Owners always have ID 0. Protected by
+	 * &drm_device.mode_config's &drm_mode_config.idr_mutex.
+	 */
 	int	lessee_id;
+
+	/**
+	 * @lessee_list:
+	 *
+	 * List of lessees of the same master. Protected by
+	 * &drm_device.mode_config's &drm_mode_config.idr_mutex.
+	 */
 	struct list_head lessee_list;
+
+	/**
+	 * @lessees:
+	 *
+	 * List of drm_masters leasing from this one. Protected by
+	 * &drm_device.mode_config's &drm_mode_config.idr_mutex.
+	 *
+	 * This master cannot be destroyed unless this list is empty as lessors
+	 * are referenced by all their lessees.
+	 */
 	struct list_head lessees;
+
+	/**
+	 * @leases:
+	 *
+	 * Objects leased to this drm_master. Protected by
+	 * &drm_device.mode_config's &drm_mode_config.idr_mutex.
+	 *
+	 * Objects are leased all together in drm_lease_create(), and are
+	 * removed all together when the lease is revoked.
+	 */
 	struct idr leases;
+
+	/**
+	 * @lessee_idr:
+	 *
+	 * All lessees under this owner (only used where lessor is NULL).
+	 * Protected by &drm_device.mode_config's &drm_mode_config.idr_mutex.
+	 */
 	struct idr lessee_idr;
 	/* private: */
 #if IS_ENABLED(CONFIG_DRM_LEGACY)
-- 
2.25.1