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

From: Lyude Paul
Date: Tue Mar 24 2020 - 15:30:07 EST

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@xxxxxxxxxx>
> > Fixes: 64e62bdf04ab ("drm/dp_mst: Remove VCPI while disabling topology
> > mgr")
> > Cc: Sean Paul <sean@xxxxxxxxxx>
> > Cc: Wayne Lin <Wayne.Lin@xxxxxxx>
> > ---
> > 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