On Thu, Jul 20, 2017 at 12:44:49PM +0100, Russell King - ARM Linux wrote:
> On Thu, Jul 20, 2017 at 12:38:53PM +0100, Russell King - ARM Linux wrote:
> > On Thu, Jul 20, 2017 at 12:04:50PM +0100, Liviu Dudau wrote:
> > > When enabling lockdep debugging on Juno platform with HDLCD and TDA998x
> > > I get the following warning from the system:
> > >
> > > [ 25.990733] ======================================================
> > > [ 25.998637] WARNING: possible circular locking dependency detected
> > > [ 26.006531] 4.13.0-rc1-00284-g28c0a682ecbf-dirty #17 Not tainted
> > > [ 26.014246] ------------------------------------------------------
> > > [ 26.022142] kworker/1:2/140 is trying to acquire lock:
> > > [ 26.029001] (&priv->audio_mutex){+.+.+.}, at: [<ffff000000d0319c>] tda998x_encoder_mode_set+0x12c/0x5a0 [tda998x]
> > > [ 26.041100]
> > > [ 26.041100] but task is already holding lock:
> > > [ 26.050436] (crtc_ww_class_mutex){+.+.+.}, at: [<ffff000000eaefe4>] drm_modeset_lock+0x64/0xf8 [drm]
> > > [ 26.061531]
> > > [ 26.061531] which lock already depends on the new lock.
> > > [ 26.061531]
> > > [ 26.075063]
> > > [ 26.075063] the existing dependency chain (in reverse order) is:
> > > [ 26.086031]
> > > [ 26.086031] -> #2 (crtc_ww_class_mutex){+.+.+.}:
> > > [ 26.095657] __lock_acquire+0x18a0/0x19b8
> > > [ 26.101918] lock_acquire+0xd0/0x2b0
> > > [ 26.107731] __ww_mutex_lock.constprop.3+0x90/0xe78
> > > [ 26.114817] ww_mutex_lock+0x54/0xe0
> > > [ 26.120672] drm_modeset_lock+0x64/0xf8 [drm]
> > > [ 26.127253] drm_helper_probe_single_connector_modes+0x7c/0x6b8 [drm_kms_helper]
> > > [ 26.136829] tda998x_connector_fill_modes+0x44/0xa8 [tda998x]
> > > [ 26.144797] drm_setup_crtcs+0x19c/0xba0 [drm_kms_helper]
> > > [ 26.152429] drm_fb_helper_initial_config+0x70/0x440 [drm_kms_helper]
> > > [ 26.161097] drm_fbdev_cma_init_with_funcs+0x94/0x168 [drm_kms_helper]
> > > [ 26.169857] drm_fbdev_cma_init+0x38/0x50 [drm_kms_helper]
> > > [ 26.177559] hdlcd_drm_bind+0x1f8/0x4a8 [hdlcd]
> > > [ 26.184310] try_to_bring_up_master+0x180/0x1e0
> > > [ 26.191043] component_master_add_with_match+0xb0/0x108
> > > [ 26.198458] hdlcd_probe+0x58/0x80 [hdlcd]
> > > [ 26.204735] platform_drv_probe+0x60/0xc0
> > > [ 26.210913] driver_probe_device+0x23c/0x2e8
> > > [ 26.217350] __driver_attach+0xd4/0xd8
> > > [ 26.223256] bus_for_each_dev+0x5c/0xa8
> > > [ 26.229232] driver_attach+0x30/0x40
> > > [ 26.234917] bus_add_driver+0x1d8/0x248
> > > [ 26.240831] driver_register+0x6c/0x118
> > > [ 26.246715] __platform_driver_register+0x54/0x60
> > > [ 26.253461] 0xffff000000e1b018
> > > [ 26.258644] do_one_initcall+0x44/0x138
> > > [ 26.264503] do_init_module+0x64/0x1d4
> > > [ 26.270238] load_module+0x1f90/0x2590
> > > [ 26.275957] SyS_finit_module+0xb0/0xc8
> > > [ 26.281765] __sys_trace_return+0x0/0x4
> > > [ 26.281767]
> > > [ 26.281767] -> #1 (crtc_ww_class_acquire){+.+.+.}:
> > > [ 26.281778] __lock_acquire+0x18a0/0x19b8
> > > [ 26.281782] lock_acquire+0xd0/0x2b0
> > > [ 26.281877] drm_modeset_acquire_init+0xa8/0xe0 [drm]
> > > [ 26.281921] drm_helper_probe_single_connector_modes+0x48/0x6b8 [drm_kms_helper]
> > > [ 26.281929] tda998x_connector_fill_modes+0x44/0xa8 [tda998x]
> > > [ 26.281970] drm_setup_crtcs+0x19c/0xba0 [drm_kms_helper]
> > > [ 26.282009] drm_fb_helper_initial_config+0x70/0x440 [drm_kms_helper]
> > > [ 26.282049] drm_fbdev_cma_init_with_funcs+0x94/0x168 [drm_kms_helper]
> > > [ 26.282088] drm_fbdev_cma_init+0x38/0x50 [drm_kms_helper]
> > > [ 26.282095] hdlcd_drm_bind+0x1f8/0x4a8 [hdlcd]
> > > [ 26.282099] try_to_bring_up_master+0x180/0x1e0
> > > [ 26.282104] component_master_add_with_match+0xb0/0x108
> > > [ 26.282110] hdlcd_probe+0x58/0x80 [hdlcd]
> > > [ 26.282114] platform_drv_probe+0x60/0xc0
> > > [ 26.282117] driver_probe_device+0x23c/0x2e8
> > > [ 26.282121] __driver_attach+0xd4/0xd8
> > > [ 26.282124] bus_for_each_dev+0x5c/0xa8
> > > [ 26.282127] driver_attach+0x30/0x40
> > > [ 26.282130] bus_add_driver+0x1d8/0x248
> > > [ 26.282134] driver_register+0x6c/0x118
> > > [ 26.282138] __platform_driver_register+0x54/0x60
> > > [ 26.282141] 0xffff000000e1b018
> > > [ 26.282145] do_one_initcall+0x44/0x138
> > > [ 26.282149] do_init_module+0x64/0x1d4
> > > [ 26.282152] load_module+0x1f90/0x2590
> > > [ 26.282156] SyS_finit_module+0xb0/0xc8
> > > [ 26.282159] __sys_trace_return+0x0/0x4
> > > [ 26.282161]
> > > [ 26.282161] -> #0 (&priv->audio_mutex){+.+.+.}:
> > > [ 26.282172] print_circular_bug+0x80/0x2e0
> > > [ 26.282176] __lock_acquire+0x15a8/0x19b8
> > > [ 26.282180] lock_acquire+0xd0/0x2b0
> > > [ 26.282184] __mutex_lock+0x78/0x8e0
> > > [ 26.282188] mutex_lock_nested+0x3c/0x50
> > > [ 26.282196] tda998x_encoder_mode_set+0x12c/0x5a0 [tda998x]
> > > [ 26.282237] drm_atomic_helper_commit_modeset_disables+0x328/0x3a0 [drm_kms_helper]
> > > [ 26.282251] malidp_atomic_commit_tail+0x44/0x6b0 [mali_dp]
> > > [ 26.282292] commit_tail+0x4c/0x80 [drm_kms_helper]
> > > [ 26.282333] drm_atomic_helper_commit+0xe8/0x180 [drm_kms_helper]
> > > [ 26.282427] drm_atomic_commit+0x54/0x70 [drm]
> > > [ 26.282467] restore_fbdev_mode_atomic+0x1f0/0x220 [drm_kms_helper]
> > > [ 26.282507] restore_fbdev_mode+0x38/0x188 [drm_kms_helper]
> > > [ 26.282547] drm_fb_helper_restore_fbdev_mode_unlocked+0x44/0xd0 [drm_kms_helper]
> > > [ 26.282586] drm_fb_helper_set_par+0x34/0x80 [drm_kms_helper]
> > > [ 26.282625] drm_fb_helper_hotplug_event.part.19+0x94/0xb0 [drm_kms_helper]
> > > [ 26.282665] drm_fb_helper_hotplug_event+0x2c/0x48 [drm_kms_helper]
> > > [ 26.282704] drm_fbdev_cma_hotplug_event+0x24/0x30 [drm_kms_helper]
> > > [ 26.282716] malidp_output_poll_changed+0x24/0x30 [mali_dp]
> > > [ 26.282757] drm_kms_helper_hotplug_event+0x34/0x40 [drm_kms_helper]
> > > [ 26.282797] output_poll_execute+0x1a0/0x1f0 [drm_kms_helper]
> > > [ 26.282803] process_one_work+0x280/0x790
> > > [ 26.282808] worker_thread+0x48/0x450
> > > [ 26.282812] kthread+0x138/0x140
> > > [ 26.282815] ret_from_fork+0x10/0x40
> > > [ 26.282817]
> > > [ 26.282817] other info that might help us debug this:
> > > [ 26.282817]
> > > [ 26.282819] Chain exists of:
> > > [ 26.282819] &priv->audio_mutex --> crtc_ww_class_acquire --> crtc_ww_class_mutex
> > > [ 26.282819]
> > > [ 26.282830] Possible unsafe locking scenario:
> > > [ 26.282830]
> > > [ 26.282832] CPU0 CPU1
> > > [ 26.282834] ---- ----
> > > [ 26.282835] lock(crtc_ww_class_mutex);
> > > [ 26.282840] lock(crtc_ww_class_acquire);
> > > [ 26.282845] lock(crtc_ww_class_mutex);
> > > [ 26.282850] lock(&priv->audio_mutex);
> > > [ 26.282854]
> > > [ 26.282854] *** DEADLOCK ***
> > > [ 26.282854]
> > > [ 26.282858] 5 locks held by kworker/1:2/140:
> > > [ 26.282859] #0: ("events"){.+.+.+}, at: [<ffff0000080f8500>] process_one_work+0x1d8/0x790
> > > [ 26.282871] #1: ((&(&dev->mode_config.output_poll_work)->work)){+.+.+.}, at: [<ffff0000080f8500>] process_one_work+0x1d8/0x790
> > > [ 26.282883] #2: (&helper->lock){+.+.+.}, at: [<ffff000000c0631c>] drm_fb_helper_restore_fbdev_mode_unlocked+0x3c/0xd0 [drm_kms_helper]
> > > [ 26.282929] #3: (crtc_ww_class_acquire){+.+.+.}, at: [<ffff000000c02d80>] restore_fbdev_mode_atomic+0x38/0x220 [drm_kms_helper]
> > > [ 26.282976] #4: (crtc_ww_class_mutex){+.+.+.}, at: [<ffff000000eaefe4>] drm_modeset_lock+0x64/0xf8 [drm]
> > > [ 26.283077]
> > > [ 26.283077] stack backtrace:
> > > [ 26.283082] CPU: 1 PID: 140 Comm: kworker/1:2 Not tainted 4.13.0-rc1-00284-g28c0a682ecbf-dirty #17
> > > [ 26.283084] Hardware name: ARM Juno development board (r0) (DT)
> > > [ 26.283127] Workqueue: events output_poll_execute [drm_kms_helper]
> > > [ 26.283131] Call trace:
> > > [ 26.283137] [<ffff00000808a778>] dump_backtrace+0x0/0x268
> > > [ 26.283142] [<ffff00000808aabc>] show_stack+0x24/0x30
> > > [ 26.283146] [<ffff000008aa36a8>] dump_stack+0xbc/0xf4
> > > [ 26.283151] [<ffff00000812f454>] print_circular_bug+0x1d4/0x2e0
> > > [ 26.283155] [<ffff000008132480>] __lock_acquire+0x15a8/0x19b8
> > > [ 26.283159] [<ffff000008133008>] lock_acquire+0xd0/0x2b0
> > > [ 26.283163] [<ffff000008aba060>] __mutex_lock+0x78/0x8e0
> > > [ 26.283168] [<ffff000008aba904>] mutex_lock_nested+0x3c/0x50
> > > [ 26.283176] [<ffff000000d0319c>] tda998x_encoder_mode_set+0x12c/0x5a0 [tda998x]
> > > [ 26.283217] [<ffff000000c00050>] drm_atomic_helper_commit_modeset_disables+0x328/0x3a0 [drm_kms_helper]
> > > [ 26.283230] [<ffff000000f1bd0c>] malidp_atomic_commit_tail+0x44/0x6b0 [mali_dp]
> > > [ 26.283271] [<ffff000000c0045c>] commit_tail+0x4c/0x80 [drm_kms_helper]
> > > [ 26.283312] [<ffff000000c00630>] drm_atomic_helper_commit+0xe8/0x180 [drm_kms_helper]
> > > [ 26.283406] [<ffff000000eb1604>] drm_atomic_commit+0x54/0x70 [drm]
> > > [ 26.283447] [<ffff000000c02f38>] restore_fbdev_mode_atomic+0x1f0/0x220 [drm_kms_helper]
> > > [ 26.283487] [<ffff000000c03cf0>] restore_fbdev_mode+0x38/0x188 [drm_kms_helper]
> > > [ 26.283526] [<ffff000000c06324>] drm_fb_helper_restore_fbdev_mode_unlocked+0x44/0xd0 [drm_kms_helper]
> > > [ 26.283566] [<ffff000000c0619c>] drm_fb_helper_set_par+0x34/0x80 [drm_kms_helper]
> > > [ 26.283606] [<ffff000000c0627c>] drm_fb_helper_hotplug_event.part.19+0x94/0xb0 [drm_kms_helper]
> > > [ 26.283645] [<ffff000000c062c4>] drm_fb_helper_hotplug_event+0x2c/0x48 [drm_kms_helper]
> > > [ 26.283685] [<ffff000000c07124>] drm_fbdev_cma_hotplug_event+0x24/0x30 [drm_kms_helper]
> > > [ 26.283697] [<ffff000000f1b44c>] malidp_output_poll_changed+0x24/0x30 [mali_dp]
> > > [ 26.283738] [<ffff000000bf5264>] drm_kms_helper_hotplug_event+0x34/0x40 [drm_kms_helper]
> > > [ 26.283779] [<ffff000000bf5480>] output_poll_execute+0x1a0/0x1f0 [drm_kms_helper]
> > > [ 26.283784] [<ffff0000080f85a8>] process_one_work+0x280/0x790
> > > [ 26.283788] [<ffff0000080f8b00>] worker_thread+0x48/0x450
> > > [ 26.283792] [<ffff000008100430>] kthread+0x138/0x140
> > > [ 26.283796] [<ffff000008083710>] ret_from_fork+0x10/0x40
> > >
> > > Fix the warning by moving the acquiring of the priv->audio_mutex in
> > > tda998x_connector_fill_modes() after the drm_helper_probe_single_connector_modes().
> > >
> > > Signed-off-by: Liviu Dudau <Liviu.Dudau@xxxxxxx>
> > > Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> > > Fixes: 02efac0fbfd5 ("drm/i2c: tda998x: remove complexity from tda998x_audio_get_eld()")
> > > ---
> > > drivers/gpu/drm/i2c/tda998x_drv.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c
> > > index d1e7ac540199..006ffeb50f34 100644
> > > --- a/drivers/gpu/drm/i2c/tda998x_drv.c
> > > +++ b/drivers/gpu/drm/i2c/tda998x_drv.c
> > > @@ -983,9 +983,9 @@ static int tda998x_connector_fill_modes(struct drm_connector *connector,
> > > struct tda998x_priv *priv = conn_to_tda998x_priv(connector);
> > > int ret;
> > >
> > > - mutex_lock(&priv->audio_mutex);
> > > ret = drm_helper_probe_single_connector_modes(connector, maxX, maxY);
> > >
> > > + mutex_lock(&priv->audio_mutex);
> >
Hi Russell,
> > This breaks the locking strategy.
TBH I don't claim that I'm familiar with the locking strategy here, I
was just parsing the warning's stack dump.
> >
> > tda998x_audio_get_eld() takes the mutex to safely read the ELD. The
> > ELD is updated in tda998x_connector_get_modes(), which is called
> > within drm_helper_probe_single_connector_modes(). Moving the mutex
> > in this way means that the update of the ELD happens outside the lock,
> > which then means there's no protection between reading and writing
> > the ELD.
First, please note that tda998x_audio_get_eld() is only involved as far
as the name of the patch that I claim to fix, it doesn't seem to be
present in the call trace. I picked that patch as the likely place where
the order of the calls was last introduced.
Second, maybe I'm missing something obvious, but drm_edid_to_eld() updates
connector->eld without taking any lock, so I don't see how
tda998x_audio_get_eld() is prevented from reading an ELD that is being
updated at the same time.
> >
> > What could be done instead is to move the locking as you have above,
> > but also move the call to drm_edid_to_eld(connector, edid) into this
> > function, also within the lock. This has the advantage that if the
> > user needs to override the EDID, then the overriden EDID is also used
> > for the ELD.
> >
> > IMHO that's more correct as the reason for overriding the EDID may be
> > to correct the audio information.
>
> Actually, scrub that idea - drm_helper_probe_single_connector_modes()
> calls drm_edid_to_eld() for these cases anyway, so we must call
> drm_helper_probe_single_connector_modes() with the audio_mutex held.
OK, so the lockdep warning is spurious?
Best regards,
Liviu
>
> --
> RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
> according to speedtest.net.
--
====================
| I would like to |
| fix the world, |
| but they're not |
| giving me the |
\ source code! /
---------------
¯\_(ツ)_/¯
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