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[212.51.149.96]) by smtp.gmail.com with ESMTPSA id q33sm3855245eda.60.2019.10.08.02.45.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 02:45:46 -0700 (PDT) Date: Tue, 8 Oct 2019 11:45:44 +0200 From: Daniel Vetter To: Sean Paul Cc: Lyude Paul , dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, Juston Li , Imre Deak , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Harry Wentland , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , David Airlie , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 03/27] drm/dp_mst: Destroy MSTBs asynchronously Message-ID: <20191008094544.GI16989@phenom.ffwll.local> Mail-Followup-To: Sean Paul , Lyude Paul , dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, Juston Li , Imre Deak , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Harry Wentland , Maarten Lankhorst , Maxime Ripard , David Airlie , linux-kernel@vger.kernel.org References: <20190903204645.25487-1-lyude@redhat.com> <20190903204645.25487-4-lyude@redhat.com> <20190925181644.GD218215@art_vandelay> <20190927133107.GQ218215@art_vandelay> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190927133107.GQ218215@art_vandelay> X-Operating-System: Linux phenom 5.2.0-2-amd64 User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 27, 2019 at 09:31:07AM -0400, Sean Paul wrote: > On Wed, Sep 25, 2019 at 04:08:22PM -0400, Lyude Paul wrote: > > On Wed, 2019-09-25 at 14:16 -0400, Sean Paul wrote: > > > On Tue, Sep 03, 2019 at 04:45:41PM -0400, Lyude Paul wrote: > > > > When reprobing an MST topology during resume, we have to account for the > > > > fact that while we were suspended it's possible that mstbs may have been > > > > removed from any ports in the topology. Since iterating downwards in the > > > > topology requires that we hold &mgr->lock, destroying MSTBs from this > > > > context would result in attempting to lock &mgr->lock a second time and > > > > deadlocking. > > > > > > > > So, fix this by first moving destruction of MSTBs into > > > > destroy_connector_work, then rename destroy_connector_work and friends > > > > to reflect that they now destroy both ports and mstbs. > > > > > > > > Changes since v1: > > > > * s/destroy_connector_list/destroy_port_list/ > > > > s/connector_destroy_lock/delayed_destroy_lock/ > > > > s/connector_destroy_work/delayed_destroy_work/ > > > > s/drm_dp_finish_destroy_branch_device/drm_dp_delayed_destroy_mstb/ > > > > s/drm_dp_finish_destroy_port/drm_dp_delayed_destroy_port/ > > > > - danvet > > > > * Use two loops in drm_dp_delayed_destroy_work() - danvet > > > > * Better explain why we need to do this - danvet > > > > * Use cancel_work_sync() instead of flush_work() - flush_work() doesn't > > > > account for work requeing > > > > > > > > Cc: Juston Li > > > > Cc: Imre Deak > > > > Cc: Ville Syrj?l? > > > > Cc: Harry Wentland > > > > Cc: Daniel Vetter > > > > Signed-off-by: Lyude Paul > > > > > > Took me a while to grok this, and I'm still not 100% confident my mental > > > model > > > is correct, so please bear with me while I ask silly questions :) > > > > > > Now that the destroy is delayed, and the port remains in the topology, is it > > > possible we will underflow the topology kref by calling put_mstb multiple > > > times? > > > It looks like that would result in a WARN from refcount.c, and wouldn't call > > > the > > > destroy function multiple times, so that's nice :) > > > > > > Similarly, is there any defense against calling get_mstb() between destroy() > > > and > > > the delayed destroy worker running? > > > > > Good question! There's only one instance where we unconditionally grab an MSTB > > ref, drm_dp_mst_topology_mgr_set_mst(), and in that location we're guaranteed > > to be the only one with access to that mstb until we drop &mgr->lock. > > Everywhere else we use drm_dp_mst_topology_try_get_mstb(), which uses > > kref_get_unless_zero() to protect against that kind of situation (and forces > > the caller to check with __must_check) Imo would be good to add this to the commit message when merging as a Q&A, just for the record. At least I like to do that with the silly-but-no-so-silly questions that come up in review. -Daniel > > Awesome, thanks for the breakdown! > > > Reviewed-by: Sean Paul > > > > > > > Sean > > > > > > > --- > > > > drivers/gpu/drm/drm_dp_mst_topology.c | 162 +++++++++++++++++--------- > > > > include/drm/drm_dp_mst_helper.h | 26 +++-- > > > > 2 files changed, 127 insertions(+), 61 deletions(-) > > > > > > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c > > > > b/drivers/gpu/drm/drm_dp_mst_topology.c > > > > index 3054ec622506..738f260d4b15 100644 > > > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c > > > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c > > > > @@ -1113,34 +1113,17 @@ static void > > > > drm_dp_destroy_mst_branch_device(struct kref *kref) > > > > struct drm_dp_mst_branch *mstb = > > > > container_of(kref, struct drm_dp_mst_branch, topology_kref); > > > > struct drm_dp_mst_topology_mgr *mgr = mstb->mgr; > > > > - struct drm_dp_mst_port *port, *tmp; > > > > - bool wake_tx = false; > > > > > > > > - mutex_lock(&mgr->lock); > > > > - list_for_each_entry_safe(port, tmp, &mstb->ports, next) { > > > > - list_del(&port->next); > > > > - drm_dp_mst_topology_put_port(port); > > > > - } > > > > - mutex_unlock(&mgr->lock); > > > > - > > > > - /* drop any tx slots msg */ > > > > - mutex_lock(&mstb->mgr->qlock); > > > > - if (mstb->tx_slots[0]) { > > > > - mstb->tx_slots[0]->state = DRM_DP_SIDEBAND_TX_TIMEOUT; > > > > - mstb->tx_slots[0] = NULL; > > > > - wake_tx = true; > > > > - } > > > > - if (mstb->tx_slots[1]) { > > > > - mstb->tx_slots[1]->state = DRM_DP_SIDEBAND_TX_TIMEOUT; > > > > - mstb->tx_slots[1] = NULL; > > > > - wake_tx = true; > > > > - } > > > > - mutex_unlock(&mstb->mgr->qlock); > > > > + INIT_LIST_HEAD(&mstb->destroy_next); > > > > > > > > - if (wake_tx) > > > > - wake_up_all(&mstb->mgr->tx_waitq); > > > > - > > > > - drm_dp_mst_put_mstb_malloc(mstb); > > > > + /* > > > > + * This can get called under mgr->mutex, so we need to perform the > > > > + * actual destruction of the mstb in another worker > > > > + */ > > > > + mutex_lock(&mgr->delayed_destroy_lock); > > > > + list_add(&mstb->destroy_next, &mgr->destroy_branch_device_list); > > > > + mutex_unlock(&mgr->delayed_destroy_lock); > > > > + schedule_work(&mgr->delayed_destroy_work); > > > > } > > > > > > > > /** > > > > @@ -1255,10 +1238,10 @@ static void drm_dp_destroy_port(struct kref *kref) > > > > * we might be holding the mode_config.mutex > > > > * from an EDID retrieval */ > > > > > > > > - mutex_lock(&mgr->destroy_connector_lock); > > > > - list_add(&port->next, &mgr->destroy_connector_list); > > > > - mutex_unlock(&mgr->destroy_connector_lock); > > > > - schedule_work(&mgr->destroy_connector_work); > > > > + mutex_lock(&mgr->delayed_destroy_lock); > > > > + list_add(&port->next, &mgr->destroy_port_list); > > > > + mutex_unlock(&mgr->delayed_destroy_lock); > > > > + schedule_work(&mgr->delayed_destroy_work); > > > > return; > > > > } > > > > /* no need to clean up vcpi > > > > @@ -2792,7 +2775,7 @@ void drm_dp_mst_topology_mgr_suspend(struct > > > > drm_dp_mst_topology_mgr *mgr) > > > > DP_MST_EN | DP_UPSTREAM_IS_SRC); > > > > mutex_unlock(&mgr->lock); > > > > flush_work(&mgr->work); > > > > - flush_work(&mgr->destroy_connector_work); > > > > + flush_work(&mgr->delayed_destroy_work); > > > > } > > > > EXPORT_SYMBOL(drm_dp_mst_topology_mgr_suspend); > > > > > > > > @@ -3740,34 +3723,104 @@ static void drm_dp_tx_work(struct work_struct > > > > *work) > > > > mutex_unlock(&mgr->qlock); > > > > } > > > > > > > > -static void drm_dp_destroy_connector_work(struct work_struct *work) > > > > +static inline void > > > > +drm_dp_delayed_destroy_port(struct drm_dp_mst_port *port) > > > > { > > > > - struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct > > > > drm_dp_mst_topology_mgr, destroy_connector_work); > > > > - struct drm_dp_mst_port *port; > > > > - bool send_hotplug = false; > > > > + port->mgr->cbs->destroy_connector(port->mgr, port->connector); > > > > + > > > > + drm_dp_port_teardown_pdt(port, port->pdt); > > > > + port->pdt = DP_PEER_DEVICE_NONE; > > > > + > > > > + drm_dp_mst_put_port_malloc(port); > > > > +} > > > > + > > > > +static inline void > > > > +drm_dp_delayed_destroy_mstb(struct drm_dp_mst_branch *mstb) > > > > +{ > > > > + struct drm_dp_mst_topology_mgr *mgr = mstb->mgr; > > > > + struct drm_dp_mst_port *port, *tmp; > > > > + bool wake_tx = false; > > > > + > > > > + mutex_lock(&mgr->lock); > > > > + list_for_each_entry_safe(port, tmp, &mstb->ports, next) { > > > > + list_del(&port->next); > > > > + drm_dp_mst_topology_put_port(port); > > > > + } > > > > + mutex_unlock(&mgr->lock); > > > > + > > > > + /* drop any tx slots msg */ > > > > + mutex_lock(&mstb->mgr->qlock); > > > > + if (mstb->tx_slots[0]) { > > > > + mstb->tx_slots[0]->state = DRM_DP_SIDEBAND_TX_TIMEOUT; > > > > + mstb->tx_slots[0] = NULL; > > > > + wake_tx = true; > > > > + } > > > > + if (mstb->tx_slots[1]) { > > > > + mstb->tx_slots[1]->state = DRM_DP_SIDEBAND_TX_TIMEOUT; > > > > + mstb->tx_slots[1] = NULL; > > > > + wake_tx = true; > > > > + } > > > > + mutex_unlock(&mstb->mgr->qlock); > > > > + > > > > + if (wake_tx) > > > > + wake_up_all(&mstb->mgr->tx_waitq); > > > > + > > > > + drm_dp_mst_put_mstb_malloc(mstb); > > > > +} > > > > + > > > > +static void drm_dp_delayed_destroy_work(struct work_struct *work) > > > > +{ > > > > + struct drm_dp_mst_topology_mgr *mgr = > > > > + container_of(work, struct drm_dp_mst_topology_mgr, > > > > + delayed_destroy_work); > > > > + bool send_hotplug = false, go_again; > > > > + > > > > /* > > > > * Not a regular list traverse as we have to drop the destroy > > > > - * connector lock before destroying the connector, to avoid AB->BA > > > > + * connector lock before destroying the mstb/port, to avoid AB->BA > > > > * ordering between this lock and the config mutex. > > > > */ > > > > - for (;;) { > > > > - mutex_lock(&mgr->destroy_connector_lock); > > > > - port = list_first_entry_or_null(&mgr->destroy_connector_list, > > > > struct drm_dp_mst_port, next); > > > > - if (!port) { > > > > - mutex_unlock(&mgr->destroy_connector_lock); > > > > - break; > > > > + do { > > > > + go_again = false; > > > > + > > > > + for (;;) { > > > > + struct drm_dp_mst_branch *mstb; > > > > + > > > > + mutex_lock(&mgr->delayed_destroy_lock); > > > > + mstb = list_first_entry_or_null(&mgr- > > > > >destroy_branch_device_list, > > > > + struct > > > > drm_dp_mst_branch, > > > > + destroy_next); > > > > + if (mstb) > > > > + list_del(&mstb->destroy_next); > > > > + mutex_unlock(&mgr->delayed_destroy_lock); > > > > + > > > > + if (!mstb) > > > > + break; > > > > + > > > > + drm_dp_delayed_destroy_mstb(mstb); > > > > + go_again = true; > > > > } > > > > - list_del(&port->next); > > > > - mutex_unlock(&mgr->destroy_connector_lock); > > > > > > > > - mgr->cbs->destroy_connector(mgr, port->connector); > > > > + for (;;) { > > > > + struct drm_dp_mst_port *port; > > > > > > > > - drm_dp_port_teardown_pdt(port, port->pdt); > > > > - port->pdt = DP_PEER_DEVICE_NONE; > > > > + mutex_lock(&mgr->delayed_destroy_lock); > > > > + port = list_first_entry_or_null(&mgr- > > > > >destroy_port_list, > > > > + struct > > > > drm_dp_mst_port, > > > > + next); > > > > + if (port) > > > > + list_del(&port->next); > > > > + mutex_unlock(&mgr->delayed_destroy_lock); > > > > + > > > > + if (!port) > > > > + break; > > > > + > > > > + drm_dp_delayed_destroy_port(port); > > > > + send_hotplug = true; > > > > + go_again = true; > > > > + } > > > > + } while (go_again); > > > > > > > > - drm_dp_mst_put_port_malloc(port); > > > > - send_hotplug = true; > > > > - } > > > > if (send_hotplug) > > > > drm_kms_helper_hotplug_event(mgr->dev); > > > > } > > > > @@ -3957,12 +4010,13 @@ int drm_dp_mst_topology_mgr_init(struct > > > > drm_dp_mst_topology_mgr *mgr, > > > > mutex_init(&mgr->lock); > > > > mutex_init(&mgr->qlock); > > > > mutex_init(&mgr->payload_lock); > > > > - mutex_init(&mgr->destroy_connector_lock); > > > > + mutex_init(&mgr->delayed_destroy_lock); > > > > INIT_LIST_HEAD(&mgr->tx_msg_downq); > > > > - INIT_LIST_HEAD(&mgr->destroy_connector_list); > > > > + INIT_LIST_HEAD(&mgr->destroy_port_list); > > > > + INIT_LIST_HEAD(&mgr->destroy_branch_device_list); > > > > INIT_WORK(&mgr->work, drm_dp_mst_link_probe_work); > > > > INIT_WORK(&mgr->tx_work, drm_dp_tx_work); > > > > - INIT_WORK(&mgr->destroy_connector_work, > > > > drm_dp_destroy_connector_work); > > > > + INIT_WORK(&mgr->delayed_destroy_work, drm_dp_delayed_destroy_work); > > > > init_waitqueue_head(&mgr->tx_waitq); > > > > mgr->dev = dev; > > > > mgr->aux = aux; > > > > @@ -4005,7 +4059,7 @@ void drm_dp_mst_topology_mgr_destroy(struct > > > > drm_dp_mst_topology_mgr *mgr) > > > > { > > > > drm_dp_mst_topology_mgr_set_mst(mgr, false); > > > > flush_work(&mgr->work); > > > > - flush_work(&mgr->destroy_connector_work); > > > > + cancel_work_sync(&mgr->delayed_destroy_work); > > > > mutex_lock(&mgr->payload_lock); > > > > kfree(mgr->payloads); > > > > mgr->payloads = NULL; > > > > diff --git a/include/drm/drm_dp_mst_helper.h > > > > b/include/drm/drm_dp_mst_helper.h > > > > index fc349204a71b..4a4507fe928d 100644 > > > > --- a/include/drm/drm_dp_mst_helper.h > > > > +++ b/include/drm/drm_dp_mst_helper.h > > > > @@ -143,6 +143,12 @@ struct drm_dp_mst_branch { > > > > */ > > > > struct kref malloc_kref; > > > > > > > > + /** > > > > + * @destroy_next: linked-list entry used by > > > > + * drm_dp_delayed_destroy_work() > > > > + */ > > > > + struct list_head destroy_next; > > > > + > > > > u8 rad[8]; > > > > u8 lct; > > > > int num_ports; > > > > @@ -575,18 +581,24 @@ struct drm_dp_mst_topology_mgr { > > > > struct work_struct tx_work; > > > > > > > > /** > > > > - * @destroy_connector_list: List of to be destroyed connectors. > > > > + * @destroy_port_list: List of to be destroyed connectors. > > > > + */ > > > > + struct list_head destroy_port_list; > > > > + /** > > > > + * @destroy_branch_device_list: List of to be destroyed branch > > > > + * devices. > > > > */ > > > > - struct list_head destroy_connector_list; > > > > + struct list_head destroy_branch_device_list; > > > > /** > > > > - * @destroy_connector_lock: Protects @connector_list. > > > > + * @delayed_destroy_lock: Protects @destroy_port_list and > > > > + * @destroy_branch_device_list. > > > > */ > > > > - struct mutex destroy_connector_lock; > > > > + struct mutex delayed_destroy_lock; > > > > /** > > > > - * @destroy_connector_work: Work item to destroy connectors. Needed to > > > > - * avoid locking inversion. > > > > + * @delayed_destroy_work: Work item to destroy MST port and branch > > > > + * devices, needed to avoid locking inversion. > > > > */ > > > > - struct work_struct destroy_connector_work; > > > > + struct work_struct delayed_destroy_work; > > > > }; > > > > > > > > int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr, > > > > -- > > > > 2.21.0 > > > > > > -- > > Cheers, > > Lyude Paul > > > > -- > Sean Paul, Software Engineer, Google / Chromium OS -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch