Re: [PATCH] backlight: Avoid double fbcon backlight handling

[joeyli <jlee@suse.com>]

On Thu, Jun 30, 2016 at 12:30:56PM +0100, Chris Wilson wrote:
> Backlights controlled by i915.ko and only associated with its connectors
> and also only associated with the intel_drmfb fbcon, controlled by
> i915.ko. In this situation, we already handle adjusting the backlight
> when the fbcon is blanked/unblanked and do not require backlight trying
> to do the same.
> 
> Attempting to register with the fbdev as a client causes lockdep to warn
> about a dependency cycle:
> 
> [   18.983763] ===========================
> [   18.983763] [ INFO: possible circular locking dependency detected ]
> [   18.983766] 4.7.0-rc5+ #524 Tainted: G           O
> [   18.983767] -------------------------------------------------------
> [   18.983767] kworker/u8:0/6 is trying to acquire lock:
> [   18.983777]  (&dev->mode_config.mutex){+.+.+.}, at: [<ffffffff815afde0>] drm_modeset_lock_all+0x40/0x120
> [   18.983777]
>                but task is already holding lock:
> [   18.983782]  ((fb_notifier_list).rwsem){++++.+}, at: [<ffffffff810ac195>] __blocking_notifier_call_chain+0x35/0x70
> [   18.983783]
>                which lock already depends on the new lock.
> 
> [   18.983783]
>                the existing dependency chain (in reverse order) is:
> [   18.983785]
>                -> #1 ((fb_notifier_list).rwsem){++++.+}:
> [   18.983789]        [<ffffffff810df611>] lock_acquire+0xb1/0x200
> [   18.983792]        [<ffffffff819a55b4>] down_write+0x44/0x80
> [   18.983795]        [<ffffffff810abf91>] blocking_notifier_chain_register+0x21/0xb0
> [   18.983798]        [<ffffffff814c7448>] fb_register_client+0x18/0x20
> [   18.983800]        [<ffffffff814c6c86>] backlight_device_register+0x136/0x260
> [   18.983852]        [<ffffffffa0127eb2>] intel_backlight_device_register+0xa2/0x160 [i915]
> [   18.983892]        [<ffffffffa00f46be>] intel_connector_register+0xe/0x10 [i915]
> [   18.983932]        [<ffffffffa0112bfb>] intel_dp_connector_register+0x1b/0x80 [i915]
> [   18.983936]        [<ffffffff8159dfea>] drm_connector_register+0x4a/0x80
> [   18.983938]        [<ffffffff8159fe44>] drm_connector_register_all+0x64/0xf0
> [   18.983940]        [<ffffffff815a2a64>] drm_modeset_register_all+0x174/0x1c0
> [   18.983942]        [<ffffffff81599b72>] drm_dev_register+0xc2/0xd0
> [   18.983976]        [<ffffffffa00621d7>] i915_driver_load+0x1547/0x2200 [i915]
> [   18.984010]        [<ffffffffa006d80f>] i915_pci_probe+0x4f/0x70 [i915]
> [   18.984014]        [<ffffffff814a2135>] local_pci_probe+0x45/0xa0
> [   18.984015]        [<ffffffff814a349b>] pci_device_probe+0xdb/0x130
> [   18.984018]        [<ffffffff815c07e3>] driver_probe_device+0x223/0x440
> [   18.984020]        [<ffffffff815c0ad5>] __driver_attach+0xd5/0x100
> [   18.984022]        [<ffffffff815be386>] bus_for_each_dev+0x66/0xa0
> [   18.984023]        [<ffffffff815c002e>] driver_attach+0x1e/0x20
> [   18.984025]        [<ffffffff815bf9be>] bus_add_driver+0x1ee/0x280
> [   18.984028]        [<ffffffff815c1810>] driver_register+0x60/0xe0
> [   18.984030]        [<ffffffff814a1a10>] __pci_register_driver+0x60/0x70
> [   18.984063]        [<ffffffffa01a905b>] i915_init+0x5b/0x62 [i915]
> [   18.984067]        [<ffffffff8100042d>] do_one_initcall+0x3d/0x150
> [   18.984070]        [<ffffffff811a935b>] do_init_module+0x5f/0x1d9
> [   18.984073]        [<ffffffff81124416>] load_module+0x20e6/0x27e0
> [   18.984075]        [<ffffffff81124d63>] SYSC_finit_module+0xc3/0xf0
> [   18.984076]        [<ffffffff81124dae>] SyS_finit_module+0xe/0x10
> [   18.984079]        [<ffffffff819a83a9>] entry_SYSCALL_64_fastpath+0x1c/0xac
> [   18.984081]
>                -> #0 (&dev->mode_config.mutex){+.+.+.}:
> [   18.984083]        [<ffffffff810df0ac>] __lock_acquire+0x10fc/0x1260
> [   18.984085]        [<ffffffff810df611>] lock_acquire+0xb1/0x200
> [   18.984088]        [<ffffffff819a3097>] mutex_lock_nested+0x67/0x3c0
> [   18.984090]        [<ffffffff815afde0>] drm_modeset_lock_all+0x40/0x120
> [   18.984093]        [<ffffffff8158f79b>] drm_fb_helper_restore_fbdev_mode_unlocked+0x2b/0x80
> [   18.984095]        [<ffffffff8158f81d>] drm_fb_helper_set_par+0x2d/0x50
> [   18.984134]        [<ffffffffa0105f7a>] intel_fbdev_set_par+0x1a/0x60 [i915]
> [   18.984136]        [<ffffffff814c13c6>] fbcon_init+0x586/0x610
> [   18.984139]        [<ffffffff8154d16a>] visual_init+0xca/0x130
> [   18.984141]        [<ffffffff8154e611>] do_bind_con_driver+0x1c1/0x3a0
> [   18.984143]        [<ffffffff8154eaf6>] do_take_over_console+0x116/0x180
> [   18.984145]        [<ffffffff814bd3a7>] do_fbcon_takeover+0x57/0xb0
> [   18.984147]        [<ffffffff814c1e48>] fbcon_event_notify+0x658/0x750
> [   18.984150]        [<ffffffff810abcae>] notifier_call_chain+0x3e/0xb0
> [   18.984152]        [<ffffffff810ac1ad>] __blocking_notifier_call_chain+0x4d/0x70
> [   18.984154]        [<ffffffff810ac1e6>] blocking_notifier_call_chain+0x16/0x20
> [   18.984156]        [<ffffffff814c748b>] fb_notifier_call_chain+0x1b/0x20
> [   18.984158]        [<ffffffff814c86b1>] register_framebuffer+0x251/0x330
> [   18.984160]        [<ffffffff8158fa9f>] drm_fb_helper_initial_config+0x25f/0x3f0
> [   18.984199]        [<ffffffffa0106b48>] intel_fbdev_initial_config+0x18/0x30 [i915]
> [   18.984201]        [<ffffffff810adfd8>] async_run_entry_fn+0x48/0x150
> [   18.984203]        [<ffffffff810a3947>] process_one_work+0x1e7/0x750
> [   18.984205]        [<ffffffff810a3efb>] worker_thread+0x4b/0x4f0
> [   18.984207]        [<ffffffff810aad4f>] kthread+0xef/0x110
> [   18.984208]        [<ffffffff819a85ef>] ret_from_fork+0x1f/0x40
> [   18.984209]
>                other info that might help us debug this:
> 
> [   18.984210]  Possible unsafe locking scenario:
> 
> [   18.984210]        CPU0                    CPU1
> [   18.984211]        ----                    ----
> [   18.984212]   lock((fb_notifier_list).rwsem);
> [   18.984213]                                lock(&dev->mode_config.mutex);
> [   18.984215]                                lock((fb_notifier_list).rwsem);
> [   18.984216]   lock(&dev->mode_config.mutex);
> [   18.984216]
>                 *** DEADLOCK ***
> 
> [   18.984217] 6 locks held by kworker/u8:0/6:
> [   18.984220]  #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff810a38c9>] process_one_work+0x169/0x750
> [   18.984223]  #1:  ((&entry->work)){+.+.+.}, at: [<ffffffff810a38c9>] process_one_work+0x169/0x750
> [   18.984227]  #2:  (registration_lock){+.+.+.}, at: [<ffffffff814c8487>] register_framebuffer+0x27/0x330
> [   18.984231]  #3:  (console_lock){+.+.+.}, at: [<ffffffff814c86ce>] register_framebuffer+0x26e/0x330
> [   18.984234]  #4:  (&fb_info->lock){+.+.+.}, at: [<ffffffff814c78dd>] lock_fb_info+0x1d/0x40
> [   18.984238]  #5:  ((fb_notifier_list).rwsem){++++.+}, at: [<ffffffff810ac195>] __blocking_notifier_call_chain+0x35/0x70
> [   18.984238]
>                stack backtrace:
> [   18.984241] CPU: 2 PID: 6 Comm: kworker/u8:0 Tainted: G           O    4.7.0-rc5+ #524
> [   18.984242] Hardware name: Intel Corp. Broxton P/NOTEBOOK, BIOS APLKRVPA.X64.0138.B33.1606250842 06/25/2016
> [   18.984244] Workqueue: events_unbound async_run_entry_fn
> [   18.984248]  0000000000000000 ffff8800758577f0 ffffffff814507a5 ffffffff828b9900
> [   18.984250]  ffffffff828b9900 ffff880075857830 ffffffff810dc6fa ffff880075857880
> [   18.984252]  ffff88007584d688 0000000000000005 0000000000000006 ffff88007584d6b0
> [   18.984253] Call Trace:
> [   18.984257]  [<ffffffff814507a5>] dump_stack+0x67/0x92
> [   18.984259]  [<ffffffff810dc6fa>] print_circular_bug+0x1aa/0x200
> [   18.984261]  [<ffffffff810df0ac>] __lock_acquire+0x10fc/0x1260
> [   18.984264]  [<ffffffff810df611>] lock_acquire+0xb1/0x200
> [   18.984266]  [<ffffffff815afde0>] ? drm_modeset_lock_all+0x40/0x120
> [   18.984267]  [<ffffffff815afde0>] ? drm_modeset_lock_all+0x40/0x120
> [   18.984269]  [<ffffffff819a3097>] mutex_lock_nested+0x67/0x3c0
> [   18.984271]  [<ffffffff815afde0>] ? drm_modeset_lock_all+0x40/0x120
> [   18.984273]  [<ffffffff810fa85f>] ? rcu_read_lock_sched_held+0x7f/0x90
> [   18.984276]  [<ffffffff81208218>] ? kmem_cache_alloc_trace+0x248/0x2b0
> [   18.984277]  [<ffffffff815afdc5>] ? drm_modeset_lock_all+0x25/0x120
> [   18.984279]  [<ffffffff815afde0>] drm_modeset_lock_all+0x40/0x120
> [   18.984281]  [<ffffffff8158f79b>] drm_fb_helper_restore_fbdev_mode_unlocked+0x2b/0x80
> [   18.984283]  [<ffffffff8158f81d>] drm_fb_helper_set_par+0x2d/0x50
> [   18.984322]  [<ffffffffa0105f7a>] intel_fbdev_set_par+0x1a/0x60 [i915]
> [   18.984324]  [<ffffffff814c13c6>] fbcon_init+0x586/0x610
> [   18.984326]  [<ffffffff8154d16a>] visual_init+0xca/0x130
> [   18.984328]  [<ffffffff8154e611>] do_bind_con_driver+0x1c1/0x3a0
> [   18.984330]  [<ffffffff8154eaf6>] do_take_over_console+0x116/0x180
> [   18.984332]  [<ffffffff814bd3a7>] do_fbcon_takeover+0x57/0xb0
> [   18.984334]  [<ffffffff814c1e48>] fbcon_event_notify+0x658/0x750
> [   18.984336]  [<ffffffff810abcae>] notifier_call_chain+0x3e/0xb0
> [   18.984338]  [<ffffffff810ac1ad>] __blocking_notifier_call_chain+0x4d/0x70
> [   18.984340]  [<ffffffff810ac1e6>] blocking_notifier_call_chain+0x16/0x20
> [   18.984342]  [<ffffffff814c748b>] fb_notifier_call_chain+0x1b/0x20
> [   18.984344]  [<ffffffff814c86b1>] register_framebuffer+0x251/0x330
> [   18.984347]  [<ffffffff815b7e8d>] ? vga_switcheroo_client_fb_set+0x5d/0x70
> [   18.984349]  [<ffffffff8158fa9f>] drm_fb_helper_initial_config+0x25f/0x3f0
> [   18.984388]  [<ffffffffa0106b48>] intel_fbdev_initial_config+0x18/0x30 [i915]
> [   18.984389]  [<ffffffff810adfd8>] async_run_entry_fn+0x48/0x150
> [   18.984391]  [<ffffffff810a3947>] process_one_work+0x1e7/0x750
> [   18.984392]  [<ffffffff810a38c9>] ? process_one_work+0x169/0x750
> [   18.984394]  [<ffffffff810a3efb>] worker_thread+0x4b/0x4f0
> [   18.984396]  [<ffffffff810a3eb0>] ? process_one_work+0x750/0x750
> [   18.984398]  [<ffffffff810aad4f>] kthread+0xef/0x110
> [   18.984401]  [<ffffffff819a85ef>] ret_from_fork+0x1f/0x40
> [   18.984402]  [<ffffffff810aac60>] ? kthread_stop+0x2e0/0x2e0
> 
> Reported-by: Imre Deak <imre.deak@intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Imre Deak <imre.deak@intel.com>
> Cc: Zhang Rui <rui.zhang@intel.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ben Skeggs <bskeggs@redhat.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: "Bruno Prémont" <bonbons@linux-vserver.org>
> Cc: Jiri Kosina <jikos@kernel.org>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Cc: "Noralf Trønnes" <noralf@tronnes.org>
> Cc: Jens Frederich <jfrederich@gmail.com>
> Cc: Daniel Drake <dsd@laptop.org>
> Cc: Jon Nettleton <jon.nettleton@gmail.com>
> Cc: Jingoo Han <jingoohan1@gmail.com>
> Cc: Lee Jones <lee.jones@linaro.org>
> Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
> Cc: Michael Hennerich <michael.hennerich@analog.com>
> Cc: Milo Kim <milo.kim@ti.com>
> Cc: Thierry Reding <thierry.reding@gmail.com>
> Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Kukjin Kim <kgene@kernel.org>
> Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
> Cc: Antonino Daplas <adaplas@gmail.com>
> Cc: linux-acpi@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: intel-gfx@lists.freedesktop.org
> Cc: nouveau@lists.freedesktop.org
> Cc: linux-renesas-soc@vger.kernel.org
> Cc: linux-fbdev@vger.kernel.org
> Cc: linux-omap@vger.kernel.org
> ---
>  drivers/acpi/acpi_video.c                            |  3 ++-
>  drivers/gpu/drm/amd/amdgpu/atombios_encoders.c       |  3 ++-
>  drivers/gpu/drm/bridge/parade-ps8622.c               |  3 ++-
>  drivers/gpu/drm/gma500/cdv_device.c                  |  3 ++-
>  drivers/gpu/drm/gma500/mdfld_device.c                |  3 ++-
>  drivers/gpu/drm/gma500/oaktrail_device.c             |  3 ++-
>  drivers/gpu/drm/gma500/psb_device.c                  |  3 ++-
>  drivers/gpu/drm/i915/intel_panel.c                   |  3 ++-
>  drivers/gpu/drm/nouveau/nouveau_backlight.c          |  6 ++++--
>  drivers/gpu/drm/omapdrm/displays/panel-dsi-cm.c      |  3 ++-
>  .../gpu/drm/omapdrm/displays/panel-sony-acx565akm.c  |  3 ++-
>  drivers/gpu/drm/radeon/atombios_encoders.c           |  3 ++-
>  drivers/gpu/drm/radeon/radeon_legacy_encoders.c      |  3 ++-
>  drivers/gpu/drm/shmobile/shmob_drm_backlight.c       |  3 ++-
>  drivers/hid/hid-picolcd_backlight.c                  |  3 ++-
>  drivers/macintosh/via-pmu-backlight.c                |  3 ++-
>  drivers/platform/x86/acer-wmi.c                      |  3 ++-
[...snip]
> diff --git a/drivers/platform/x86/acer-wmi.c b/drivers/platform/x86/acer-wmi.c
> index 79d64ea00bfb..0b17c5146175 100644
> --- a/drivers/platform/x86/acer-wmi.c
> +++ b/drivers/platform/x86/acer-wmi.c
> @@ -1419,7 +1419,8 @@ static int acer_backlight_init(struct device *dev)
>  	props.type = BACKLIGHT_PLATFORM;
>  	props.max_brightness = max_brightness;
>  	bd = backlight_device_register("acer-wmi", dev, NULL, &acer_bl_ops,
> -				       &props);
> +				       &props,
> +				       BACKLIGHT_REGISTER_FB_CLIENT);
>  	if (IS_ERR(bd)) {
>  		pr_err("Could not register Acer backlight device\n");
>  		acer_backlight_device = NULL;

For the part of acer-wmi driver.

Review-by: Lee, Chun-Yi <jlee@suse.com>


Thanks a lot!
Joey Lee