Messages in this thread | | | Subject | Re: [PATCH 2/3] drm: clarify lifetime/locking for drm_master's lease fields | From | Desmond Cheong Zhi Xi <> | Date | Thu, 22 Jul 2021 21:02:56 +0800 |
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On 22/7/21 6:35 pm, Daniel Vetter wrote: > On Thu, Jul 22, 2021 at 05:29:28PM +0800, Desmond Cheong Zhi Xi wrote: >> 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@gmail.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 > > Lessor is the lease grantor, lessee is the one receiving the lease. Maybe > clarify this with > > "Lease grantor, only set if this struct drm_master represents a lessee > holding a lease of objects from @lessor. Full owners of the device have > this set to NULL." > >> + * drm_lease_create(). Each lessee holds a reference to its lessor that > > I also figured it'd be a good idea to link to the drm_lease docs here to > explain the concepts, but alas we don't have those :-( Hence at least > define what we mean with lessor, lessee, lease and owner. >
Thanks for the suggestions, Daniel. I'll incorporate them in a v2.
Regarding the missing drm_lease docs... any reason we can't just add it in? Seems like most of the comments in drm_lease.c are almost correctly formatted too. I could clean them up, define the terms in a preamble, then add it to the v2 patch.
>> + * it releases upon being destroyed in drm_lease_destroy(). >> + * >> + * Display resource leases form a tree of &struct drm_master. All of > > For now we've limited the tree to a depth of 1, you can't create another > lease if yourself are a lease. I guess another reason to update the > drm_lease.c docs. > > So maybe add "Currently the lease tree depth is limited to 1." > >> + * 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 > > Maybe clarify to "Owners (i.e. @lessor is NULL) ..." > >> + * &drm_device.mode_config's &drm_mode_config.idr_mutex. >> + */ >> int lessee_id; >> + >> + /** >> + * @lessee_list: >> + * >> + * List of lessees of the same master. Protected by > > We try to distinguis between list entries and the list, even though it's > the same struct. So maybe > > "List entry of lessees of @lessor, where they are linked to @lessee. Not > use for owners." > >> + * &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. > > Maybe add "this list is empty of no leases have been granted." > >> + */ >> 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). > > @lessor so it's highlighted correctly > >> + * Protected by &drm_device.mode_config's &drm_mode_config.idr_mutex. >> + */ >> struct idr lessee_idr; >> /* private: */ > > With the nits addressed: > > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> > > Thanks for updating the docs! > -Daniel > >> #if IS_ENABLED(CONFIG_DRM_LEGACY) >> -- >> 2.25.1 >> >
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