Re: [PATCH] Revert "drm/dp_mst: Remove VCPI while disabling topology mgr"

[Lyude Paul <lyude@redhat.com>]

Huh? There was an alternative fix for this pushed a while ago:

8732fe46b20c ("drm/dp_mst: Fix clearing payload state on topology disable")

But I'm not seeing it in master, although it is cc'd for stable :S

On Sun, 2020-03-22 at 16:42 +0100, Jiri Kosina wrote:
> On Fri, 17 Jan 2020, Lyude Paul 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.
> 
> So I just received this very lockdep splat on 5.6-rc3 (I know, it's not 
> the latest and greatest, but I don't see anything related between 5.6-rc3 
> and Linus' HEAD).
> 
> Seems like this revert was never applied. Could this please be revisited? 
> Or has some alternative fix been comitted between 5.6-rc3 and current?
> 
> Thanks.
> 
> > [   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>
> > 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
> > 
-- 
Cheers,
	Lyude Paul (she/her)
	Associate Software Engineer at Red Hat

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