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References: <20200117205149.97262-1-lyude@redhat.com>
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From:   Sean Paul <sean@poorly.run>
Date:   Fri, 17 Jan 2020 15:53:20 -0500
Message-ID: <CAMavQK+QSbf++fEPu9WfyGR2+2QrbRN_x1f40Sz6kjw4wUP5vg@mail.gmail.com>
Subject: Re: [PATCH] Revert "drm/dp_mst: Remove VCPI while disabling topology mgr"
To:     Lyude Paul <lyude@redhat.com>
Cc:     dri-devel <dri-devel@lists.freedesktop.org>,
        Wayne Lin <Wayne.Lin@amd.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        LKML <linux-kernel@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Fri, Jan 17, 2020 at 3:51 PM Lyude Paul <lyude@redhat.com> wrote:
>
> This reverts commit 64e62bdf04ab8529f45ed0a85122c703035dec3a.
>
> This commit ends up causing some lockdep splats due to trying to grab the
> payload lock while holding the mgr's lock:
>
> [   54.010099]
> [   54.011765] ======================================================
> [   54.018670] WARNING: possible circular locking dependency detected
> [   54.025577] 5.5.0-rc6-02274-g77381c23ee63 #47 Not tainted
> [   54.031610] ------------------------------------------------------
> [   54.038516] kworker/1:6/1040 is trying to acquire lock:
> [   54.044354] ffff888272af3228 (&mgr->payload_lock){+.+.}, at:
> drm_dp_mst_topology_mgr_set_mst+0x218/0x2e4
> [   54.054957]
> [   54.054957] but task is already holding lock:
> [   54.061473] ffff888272af3060 (&mgr->lock){+.+.}, at:
> drm_dp_mst_topology_mgr_set_mst+0x3c/0x2e4
> [   54.071193]
> [   54.071193] which lock already depends on the new lock.
> [   54.071193]
> [   54.080334]
> [   54.080334] the existing dependency chain (in reverse order) is:
> [   54.088697]
> [   54.088697] -> #1 (&mgr->lock){+.+.}:
> [   54.094440]        __mutex_lock+0xc3/0x498
> [   54.099015]        drm_dp_mst_topology_get_port_validated+0x25/0x80
> [   54.106018]        drm_dp_update_payload_part1+0xa2/0x2e2
> [   54.112051]        intel_mst_pre_enable_dp+0x144/0x18f
> [   54.117791]        intel_encoders_pre_enable+0x63/0x70
> [   54.123532]        hsw_crtc_enable+0xa1/0x722
> [   54.128396]        intel_update_crtc+0x50/0x194
> [   54.133455]        skl_commit_modeset_enables+0x40c/0x540
> [   54.139485]        intel_atomic_commit_tail+0x5f7/0x130d
> [   54.145418]        intel_atomic_commit+0x2c8/0x2d8
> [   54.150770]        drm_atomic_helper_set_config+0x5a/0x70
> [   54.156801]        drm_mode_setcrtc+0x2ab/0x833
> [   54.161862]        drm_ioctl+0x2e5/0x424
> [   54.166242]        vfs_ioctl+0x21/0x2f
> [   54.170426]        do_vfs_ioctl+0x5fb/0x61e
> [   54.175096]        ksys_ioctl+0x55/0x75
> [   54.179377]        __x64_sys_ioctl+0x1a/0x1e
> [   54.184146]        do_syscall_64+0x5c/0x6d
> [   54.188721]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [   54.194946]
> [   54.194946] -> #0 (&mgr->payload_lock){+.+.}:
> [   54.201463]
> [   54.201463] other info that might help us debug this:
> [   54.201463]
> [   54.210410]  Possible unsafe locking scenario:
> [   54.210410]
> [   54.217025]        CPU0                    CPU1
> [   54.222082]        ----                    ----
> [   54.227138]   lock(&mgr->lock);
> [   54.230643]                                lock(&mgr->payload_lock);
> [   54.237742]                                lock(&mgr->lock);
> [   54.244062]   lock(&mgr->payload_lock);
> [   54.248346]
> [   54.248346]  *** DEADLOCK ***
> [   54.248346]
> [   54.254959] 7 locks held by kworker/1:6/1040:
> [   54.259822]  #0: ffff888275c4f528 ((wq_completion)events){+.+.},
> at: worker_thread+0x455/0x6e2
> [   54.269451]  #1: ffffc9000119beb0
> ((work_completion)(&(&dev_priv->hotplug.hotplug_work)->work)){+.+.},
> at: worker_thread+0x455/0x6e2
> [   54.282768]  #2: ffff888272a403f0 (&dev->mode_config.mutex){+.+.},
> at: i915_hotplug_work_func+0x4b/0x2be
> [   54.293368]  #3: ffffffff824fc6c0 (drm_connector_list_iter){.+.+},
> at: i915_hotplug_work_func+0x17e/0x2be
> [   54.304061]  #4: ffffc9000119bc58 (crtc_ww_class_acquire){+.+.},
> at: drm_helper_probe_detect_ctx+0x40/0xfd
> [   54.314855]  #5: ffff888272a40470 (crtc_ww_class_mutex){+.+.}, at:
> drm_modeset_lock+0x74/0xe2
> [   54.324385]  #6: ffff888272af3060 (&mgr->lock){+.+.}, at:
> drm_dp_mst_topology_mgr_set_mst+0x3c/0x2e4
> [   54.334597]
> [   54.334597] stack backtrace:
> [   54.339464] CPU: 1 PID: 1040 Comm: kworker/1:6 Not tainted
> 5.5.0-rc6-02274-g77381c23ee63 #47
> [   54.348893] Hardware name: Google Fizz/Fizz, BIOS
> Google_Fizz.10139.39.0 01/04/2018
> [   54.357451] Workqueue: events i915_hotplug_work_func
> [   54.362995] Call Trace:
> [   54.365724]  dump_stack+0x71/0x9c
> [   54.369427]  check_noncircular+0x91/0xbc
> [   54.373809]  ? __lock_acquire+0xc9e/0xf66
> [   54.378286]  ? __lock_acquire+0xc9e/0xf66
> [   54.382763]  ? lock_acquire+0x175/0x1ac
> [   54.387048]  ? drm_dp_mst_topology_mgr_set_mst+0x218/0x2e4
> [   54.393177]  ? __mutex_lock+0xc3/0x498
> [   54.397362]  ? drm_dp_mst_topology_mgr_set_mst+0x218/0x2e4
> [   54.403492]  ? drm_dp_mst_topology_mgr_set_mst+0x218/0x2e4
> [   54.409620]  ? drm_dp_dpcd_access+0xd9/0x101
> [   54.414390]  ? drm_dp_mst_topology_mgr_set_mst+0x218/0x2e4
> [   54.420517]  ? drm_dp_mst_topology_mgr_set_mst+0x218/0x2e4
> [   54.426645]  ? intel_digital_port_connected+0x34d/0x35c
> [   54.432482]  ? intel_dp_detect+0x227/0x44e
> [   54.437056]  ? ww_mutex_lock+0x49/0x9a
> [   54.441242]  ? drm_helper_probe_detect_ctx+0x75/0xfd
> [   54.446789]  ? intel_encoder_hotplug+0x4b/0x97
> [   54.451752]  ? intel_ddi_hotplug+0x61/0x2e0
> [   54.456423]  ? mark_held_locks+0x53/0x68
> [   54.460803]  ? _raw_spin_unlock_irqrestore+0x3a/0x51
> [   54.466347]  ? lockdep_hardirqs_on+0x187/0x1a4
> [   54.471310]  ? drm_connector_list_iter_next+0x89/0x9a
> [   54.476953]  ? i915_hotplug_work_func+0x206/0x2be
> [   54.482208]  ? worker_thread+0x4d5/0x6e2
> [   54.486587]  ? worker_thread+0x455/0x6e2
> [   54.490966]  ? queue_work_on+0x64/0x64
> [   54.495151]  ? kthread+0x1e9/0x1f1
> [   54.498946]  ? queue_work_on+0x64/0x64
> [   54.503130]  ? kthread_unpark+0x5e/0x5e
> [   54.507413]  ? ret_from_fork+0x3a/0x50
>
> The proper fix for this is probably cleanup the VCPI allocations when we're
> enabling the topology, or on the first payload allocation. For now though,
> let's just revert.
>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Fixes: 64e62bdf04ab ("drm/dp_mst: Remove VCPI while disabling topology mgr")
> Cc: Sean Paul <sean@poorly.run>

Reviewed-by: Sean Paul <sean@poorly.run>

> Cc: Wayne Lin <Wayne.Lin@amd.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 13 -------------
>  1 file changed, 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 4b74193b89ce..0c585f2bbb69 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3481,7 +3481,6 @@ static int drm_dp_get_vc_payload_bw(u8 dp_link_bw, u8  dp_link_count)
>  int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool mst_state)
>  {
>         int ret = 0;
> -       int i = 0;
>         struct drm_dp_mst_branch *mstb = NULL;
>
>         mutex_lock(&mgr->lock);
> @@ -3542,22 +3541,10 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
>                 /* this can fail if the device is gone */
>                 drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL, 0);
>                 ret = 0;
> -               mutex_lock(&mgr->payload_lock);
>                 memset(mgr->payloads, 0, mgr->max_payloads * sizeof(struct drm_dp_payload));
>                 mgr->payload_mask = 0;
>                 set_bit(0, &mgr->payload_mask);
> -               for (i = 0; i < mgr->max_payloads; i++) {
> -                       struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
> -
> -                       if (vcpi) {
> -                               vcpi->vcpi = 0;
> -                               vcpi->num_slots = 0;
> -                       }
> -                       mgr->proposed_vcpis[i] = NULL;
> -               }
>                 mgr->vcpi_mask = 0;
> -               mutex_unlock(&mgr->payload_lock);
> -
>                 mgr->payload_id_table_cleared = false;
>         }
>
> --
> 2.24.1
>