Hi,
I mentioned this internally, but wanted to get it on the list,
I ran the hdmi kunit tests with LOCKDEP and WW_MUTEX_SLOWPATH enabled
and hit some issues.
With the slowpath we get the occasional EDEADLK to test the paths are
doing things right, I think you should handle EDEADLK in the tests
with a retry loop.
meanwhile lockdep said
[ 64.885157] KTAP version 1
[ 64.886206] 1..2
[ 64.887950] KTAP version 1
[ 64.888738] # Subtest: drm_atomic_helper_connector_hdmi_check
[ 64.890271] # module: drm_hdmi_state_helper_test
[ 64.890291] 1..22
[ 64.898189] ======================================================
[ 64.899995] WARNING: possible circular locking dependency detected
[ 64.901475] 6.12.0-rc5+ #2 Tainted: G N
[ 64.902928] ------------------------------------------------------
[ 64.904543] kunit_try_catch/1962 is trying to acquire lock:
[ 64.906062] ffff502cc9c1c488 (&dev->mode_config.mutex){+.+.}-{3:3},
at: drm_test_check_broadcast_rgb_auto_cea_mode+0xb0/0x460
[drm_hdmi_state_helper_test]
[ 64.909764]
but task is already holding lock:
[ 64.911408] ffff502cd0aa03f0 (crtc_ww_class_acquire){+.+.}-{0:0},
at: drm_kunit_helper_acquire_ctx_alloc+0x64/0x100 [drm_kunit_helpers]
[ 64.915352]
which lock already depends on the new lock.
[ 64.917596]
the existing dependency chain (in reverse order) is:
[ 64.919596]
-> #1 (crtc_ww_class_acquire){+.+.}-{0:0}:
[ 64.921408] __lock_acquire+0x50c/0xb00
[ 64.922690] lock_acquire.part.0+0xf0/0x270
[ 64.923955] lock_acquire+0x90/0x180
[ 64.925099] drm_modeset_acquire_init+0xd4/0x138
[ 64.926526] drm_helper_probe_single_connector_modes+0x70/0x638
[ 64.929138] set_connector_edid.isra.0+0x70/0x118
[drm_hdmi_state_helper_test]
[ 64.931267]
drm_atomic_helper_connector_hdmi_init+0x20c/0x3a0
[drm_hdmi_state_helper_test]
[ 64.933616]
drm_test_check_broadcast_rgb_auto_cea_mode+0x50/0x460
[drm_hdmi_state_helper_test]
[ 64.936099] kunit_try_run_case+0x74/0x170 [kunit]
[ 64.937518] kunit_generic_run_threadfn_adapter+0x30/0x60 [kunit]
[ 64.939325] kthread+0x100/0x118
[ 64.940364] ret_from_fork+0x10/0x20
[ 64.941513]
-> #0 (&dev->mode_config.mutex){+.+.}-{3:3}:
[ 64.943305] check_prev_add+0x114/0x9d8
[ 64.944459] validate_chain+0x46c/0x500
[ 64.946249] __lock_acquire+0x50c/0xb00
[ 64.947421] lock_acquire.part.0+0xf0/0x270
[ 64.948690] lock_acquire+0x90/0x180
[ 64.949801] __mutex_lock+0xc0/0x430
[ 64.950964] mutex_lock_nested+0x2c/0x40
[ 64.952160]
drm_test_check_broadcast_rgb_auto_cea_mode+0xb0/0x460
[drm_hdmi_state_helper_test]
[ 64.954613] kunit_try_run_case+0x74/0x170 [kunit]
[ 64.956069] kunit_generic_run_threadfn_adapter+0x30/0x60 [kunit]
[ 64.957830] kthread+0x100/0x118
[ 64.958855] ret_from_fork+0x10/0x20
[ 64.960273]
other info that might help us debug this:
[ 64.962749] Possible unsafe locking scenario:
[ 64.964330] CPU0 CPU1
[ 64.965575] ---- ----
[ 64.966782] lock(crtc_ww_class_acquire);
[ 64.967881] lock(&dev->mode_config.mutex);
[ 64.969841] lock(crtc_ww_class_acquire);
[ 64.971922] lock(&dev->mode_config.mutex);
[ 64.973070]
*** DEADLOCK ***
[ 64.974634] 1 lock held by kunit_try_catch/1962:
[ 64.976040] #0: ffff502cd0aa03f0
(crtc_ww_class_acquire){+.+.}-{0:0}, at:
drm_kunit_helper_acquire_ctx_alloc+0x64/0x100 [drm_kunit_helpers]
[ 64.979943]
stack backtrace:
[ 64.981136] CPU: 2 UID: 0 PID: 1962 Comm: kunit_try_catch Tainted:
G N 6.12.0-rc5+ #2
[ 64.983577] Tainted: [N]=TEST
[ 64.984356] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
[ 64.986202] Call trace:
[ 64.986856] dump_backtrace+0xdc/0x140
[ 64.987863] show_stack+0x20/0x40
[ 64.988737] dump_stack_lvl+0x9c/0xd0
[ 64.989761] dump_stack+0x18/0x30
[ 64.990809] print_circular_bug+0xf0/0x100
[ 64.992300] check_noncircular+0x174/0x188
[ 64.993451] check_prev_add+0x114/0x9d8
[ 64.994467] validate_chain+0x46c/0x500
[ 64.995540] __lock_acquire+0x50c/0xb00
[ 64.996566] lock_acquire.part.0+0xf0/0x270
[ 64.997693] lock_acquire+0x90/0x180
[ 64.998643] __mutex_lock+0xc0/0x430
[ 64.999610] mutex_lock_nested+0x2c/0x40
[ 65.000639] drm_test_check_broadcast_rgb_auto_cea_mode+0xb0/0x460
[drm_hdmi_state_helper_test]
[ 65.002987] kunit_try_run_case+0x74/0x170 [kunit]
[ 65.004274] kunit_generic_run_threadfn_adapter+0x30/0x60 [kunit]
[ 65.006488] kthread+0x100/0x118
[ 65.007354] ret_from_fork+0x10/0x20
Dave.
