On Thu, Nov 24, 2016 at 02:40:50PM +0000, Robin Murphy wrote:
> On 24/11/16 13:49, Robin Murphy wrote:
> > On 24/11/16 13:29, Russell King - ARM Linux wrote:
> >> On Thu, Nov 24, 2016 at 01:18:39PM +0000, Robin Murphy wrote:
> >>> Hi Liviu, Russell,
> >>>
> >>> I'd been meaning to try digging into this if it hadn't gone away since I
> >>> first noticed it, but I don't really have the time and it still happens
> >>> with 4.9-rc and today's -next. Representative splat below, but in
> >>> summary what happens is that if the HDLCD fails to probe, the TDA998x
> >>> connector seems to get cleaned up twice, resulting in a NULL dereference
> >>> the second time. I got as far as sketching out the following flow from a
> >>> debug session (on the same 4.8-rc2 kernel), but I don't know nearly
> >>> enough to tell which driver is at fault:
> >>>
> >>> hdlcd_drm_bind
> >>> -> drm_fbdev_cma_init (fails)
> >>> ...
> >>> -> drm_mode_config_cleanup
> >>> ...
> >>> -> drm_connector_cleanup
> >>> -> component_unbind_all
> >>> ...
> >>> -> tda998x_unbind
> >>> -> drm_connector_cleanup (NULL connector)
> >>>
> >>> It's easily reproduced on Juno by booting arm64 defconfig with
> >>> CONFIG_CMA_SIZE_MBYTES=1 and a sufficiently large monitor connected to
> >>> warrant a >1MB framebuffer.
> >>
> >> It looks to me like a hdlcd bug.
> >>
> >> The probe path operates in this order:
> >>
> >> - allocates hdlcd - 1
> >> - allocates drm device - 2
> >> - drm_mode_config_init - 3
> >> - hdlcd_load - 4
> >> - binds all components - 5
> >> - enables runtime PM - 6
> >> - drm_vblank_init - 7
> >> - drm_mode_config_reset - 8
> >> - drm_kms_helper_poll_init - 9
> >> - drm_fbdev_cma_init - 10
> >> - drm_dev_register - 11
> >>
> >> However, the cleanup operates in this order:
> >> - drm_fbdev_cma_fini - undoes 10
> >> - drm_kms_helper_poll_fini - undoes 9
> >> - drm_mode_config_cleanup - undoes 3
> >> - drm_vblank_cleanup - undoes 7
> >> - pm_runtime_disable - undoes 6
> >> - component_unbind_all - undoes 5
> >> - drm_irq_uninstall - undoes 4
> >> - of_reserved_mem_device_release - undoes other half of 4
> >> - drm_dev_unref - undoes 2
> >>
> >> Spot the step which is out of the correct order - drm_mode_config_cleanup()
> >> is misplaced - it's reversing the actions of drm_mode_config_init(), not
> >> drm_mode_config_reset().
> >
> > Thanks for the explanation - that saves at least a day's worth of me
> > trying to understand DRM code :)
> >
> >> So, drm_mode_config_cleanup() should be much later, after step 4 has
> >> been undone, otherwise there are paths that leave various DRM objects
> >> (created by drm_mode_create_standard_properties()) referenced, and
> >> will cause problems exactly like you're seeing here.
> >
> > Liviu, can I leave this with you then?
>
> That said, I just tried the quick and obvious thing over lunch and it
> does *seem* to be OK:
Hi Robin,
Thanks for tracking this down and for providing a patch.
>
> ----->8-----
> From: Robin Murphy <robin.murphy@xxxxxxx>
> Subject: [PATCH] drm: hdlcd: Fix cleanup order
>
> If hdlcd_drm_bind() fails at drm_fbdev_cma_init(), its cleanup will call
> drm_mode_config_cleanup() as if to balance drm_mode_config_reset(). The
> net result is that drm_connector_cleanup() will clean up the active
> connectors long before component_unbind_all() gets called, so when the
> connector later tries to clean up itself after being unbound, Bad Things
> can happen:
>
> [ 4.121888] Unable to handle kernel NULL pointer dereference at
> virtual address 00000000
> [ 4.129951] pgd = ffffff80091e0000
> [ 4.133345] [00000000] *pgd=00000009ffffe003, *pud=00000009ffffe003,
> *pmd=0000000000000000
> [ 4.141613] Internal error: Oops: 96000005 [#1] PREEMPT SMP
> [ 4.147144] Modules linked in:
> [ 4.150188] CPU: 0 PID: 122 Comm: kworker/u12:2 Not tainted
> 4.8.0-rc2+ #989
> [ 4.157097] Hardware name: ARM Juno development board (r1) (DT)
> [ 4.162981] Workqueue: deferwq deferred_probe_work_func
> [ 4.168173] task: ffffffc975d93200 task.stack: ffffffc975dac000
> [ 4.174055] PC is at drm_connector_cleanup+0x58/0x1c0
> [ 4.179074] LR is at tda998x_unbind+0x24/0x40
> [ 4.183401] pc : [<ffffff80084c46f0>] lr : [<ffffff800850414c>]
> pstate: 00000045
> [ 4.190750] sp : ffffffc975dafa10
> [ 4.194041] x29: ffffffc975dafa10 x28: ffffffc9768152a8
> [ 4.199325] x27: ffffffc97ff46450 x26: ffffff8008d99000
> [ 4.204608] x25: dead000000000100 x24: dead000000000200
> [ 4.209891] x23: ffffffc976bf91e8 x22: 0000000000000000
> [ 4.215172] x21: ffffffc976bf9170 x20: ffffffc976bf9170
> [ 4.220454] x19: ffffffc976bf9018 x18: 0000000000000000
> [ 4.225737] x17: 0000000074ce71ee x16: 000000008ff5d35f
> [ 4.231019] x15: ffffffc97681e91c x14: ffffffffffffffff
> [ 4.236301] x13: ffffffc97681e185 x12: 0000000000000038
> [ 4.241583] x11: 0101010101010101 x10: 0000000000000000
> [ 4.246866] x9 : 0000000040000000 x8 : 0000000000210d00
> [ 4.252148] x7 : ffffffc97fea8c00 x6 : 000000000000001b
> [ 4.257430] x5 : ffffff80084b7b8c x4 : 0000000000000080
> [ 4.262712] x3 : ffffff8008504128 x2 : ffffffc975df3800
> [ 4.267993] x1 : 0000000000000000 x0 : 0000000000000000
> ...
> [ 4.750937] [<ffffff80084c46f0>] drm_connector_cleanup+0x58/0x1c0
> [ 4.756990] [<ffffff800850414c>] tda998x_unbind+0x24/0x40
> [ 4.762354] [<ffffff8008507918>] component_unbind.isra.4+0x28/0x50
> [ 4.768492] [<ffffff8008507a0c>] component_unbind_all+0xcc/0xd8
> [ 4.774373] [<ffffff80084d5adc>] hdlcd_drm_bind+0x234/0x418
> [ 4.779909] [<ffffff8008507b58>] try_to_bring_up_master+0x140/0x1a0
> [ 4.786133] [<ffffff8008507c50>] component_add+0x98/0x170
> [ 4.791496] [<ffffff8008504b90>] tda998x_probe+0x18/0x20
> [ 4.796774] [<ffffff80086bf914>] i2c_device_probe+0x164/0x258
> [ 4.802481] [<ffffff800850d094>] driver_probe_device+0x204/0x2b0
> [ 4.808447] [<ffffff800850d28c>] __device_attach_driver+0x9c/0xf8
> [ 4.814498] [<ffffff800850b108>] bus_for_each_drv+0x58/0x98
> [ 4.820033] [<ffffff800850cd64>] __device_attach+0xc4/0x138
> [ 4.825567] [<ffffff800850d338>] device_initial_probe+0x10/0x18
> [ 4.831446] [<ffffff800850c124>] bus_probe_device+0x94/0xa0
> [ 4.836981] [<ffffff800850c5b0>] deferred_probe_work_func+0x78/0xb0
> [ 4.843207] [<ffffff80080d2998>] process_one_work+0x118/0x378
> [ 4.848914] [<ffffff80080d2c40>] worker_thread+0x48/0x498
> [ 4.854276] [<ffffff80080d8918>] kthread+0xd0/0xe8
> [ 4.859036] [<ffffff8008082e90>] ret_from_fork+0x10/0x40
> [ 4.864314] Code: f2fbd5b9 f2fbd5b8 f8478ee0 eb17001f (f9400013)
> [ 4.870472] ---[ end trace a643cfe4ce1d838b ]---
>
> Fix this by moving the drm_mode_config_cleanup() much later such that it
> correctly balances drm_mode_config_init().
>
> Suggested-by: Russell King <linux@xxxxxxxxxxxxxxx>
> Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
Acked-by: Liviu Dudau <Liviu.Dudau@xxxxxxx>
Best regards,
Liviu
> ---
> drivers/gpu/drm/arm/hdlcd_drv.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/arm/hdlcd_drv.c
> b/drivers/gpu/drm/arm/hdlcd_drv.c
> index 59b76054edc9..1a4fff7c0a7c 100644
> --- a/drivers/gpu/drm/arm/hdlcd_drv.c
> +++ b/drivers/gpu/drm/arm/hdlcd_drv.c
> @@ -420,7 +420,6 @@ static int hdlcd_drm_bind(struct device *dev)
>
> err_fbdev:
> drm_kms_helper_poll_fini(drm);
> - drm_mode_config_cleanup(drm);
> drm_vblank_cleanup(drm);
> err_vblank:
> pm_runtime_disable(drm->dev);
> @@ -432,6 +431,7 @@ static int hdlcd_drm_bind(struct device *dev)
> drm_irq_uninstall(drm);
> of_reserved_mem_device_release(drm->dev);
> err_free:
> + drm_mode_config_cleanup(drm);
> dev_set_drvdata(dev, NULL);
> drm_dev_unref(drm);
>
> --
> 2.10.2.dirty
>
--
====================
| I would like to |
| fix the world, |
| but they're not |
| giving me the |
\ source code! /
---------------
¯\_(ツ)_/¯
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