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.
Robin.
[ 4.107349] hdlcd 7ff60000.hdlcd: failed to allocate buffer with size 7680000 [ 4.114459] hdlcd 7ff60000.hdlcd: Failed to set initial hw configuration. [ 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 [ 4.273274] [ 4.274759] Process kworker/u12:2 (pid: 122, stack limit = 0xffffffc975dac020) [ 4.281938] Stack: (0xffffffc975dafa10 to 0xffffffc975db0000) [ 4.285576] ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 0) [ 4.293602] fa00: ffffffc975dafa60 ffffff800850414c [ 4.301386] fa20: ffffffc976bf9018 ffffffc976bf9170 0000000000000000 ffffffc975df3800 [ 4.309170] fa40: ffffffc975c1e1a0 ffffffc976b14400 ffffffc976b14410 ffffff8008518784 [ 4.316954] fa60: ffffffc975dafa80 ffffff8008507918 ffffffc976bdf080 ffffffffffffffd8 [ 4.324737] fa80: ffffffc975dafaa0 ffffff8008507a0c ffffffc975c1e180 ffffffc976b14400 [ 4.332521] faa0: ffffffc975dafae0 ffffff80084d5adc ffffffc975df3800 fffffffffffffff4 [ 4.340305] fac0: ffffffc976b14410 ffffffc975df3018 ffffffc975df3018 ffffff80084d5ab4 [ 4.348089] fae0: ffffffc975dafb30 ffffff8008507b58 ffffffc976bdf080 0000000000000028 [ 4.355873] fb00: ffffff8008d3d600 0000000000000001 ffffffc975c1e180 ffffffc976bdf080 [ 4.363657] fb20: ffffffc975c1e098 ffffff80084d5428 ffffffc975dafb90 ffffff8008507c50 [ 4.371441] fb40: ffffffc975c1e180 ffffff8008d3d5f0 ffffffc976bdf080 ffffffc976b57000 [ 4.379225] fb60: ffffff8008d3d000 ffffffc976815000 ffffff8008d926c6 ffffffc976815020 [ 4.387009] fb80: ffffffc976815078 ffffffc9768152a8 ffffffc975dafbd0 ffffff8008504b90 [ 4.394793] fba0: ffffff8008d3d4e8 ffffffc976b57020 ffffffc976b57004 ffffffc976b57000 [ 4.402577] fbc0: ffffff8008504b78 ffffff80086bf8cc ffffffc975dafbe0 ffffff80086bf914 [ 4.410360] fbe0: ffffffc975dafc20 ffffff800850d094 ffffffc976b57020 ffffff8008dc4000 [ 4.418144] fc00: 0000000000000000 ffffff8008d3d448 0000000000000004 ffffff8008dc4000 [ 4.425928] fc20: ffffffc975dafc60 ffffff800850d28c ffffff8008d3d448 ffffffc975dafd00 [ 4.433711] fc40: ffffffc976b57020 0000000000000001 ffffffc975e3b400 ffffff800850b114 [ 4.441495] fc60: ffffffc975dafc90 ffffff800850b108 0000000000000000 ffffffc975dafd00 [ 4.449279] fc80: ffffff800850d1f0 0000000000000001 ffffffc975dafcd0 ffffff800850cd64 [ 4.457062] fca0: ffffffc976b57020 ffffffc976b57080 ffffff8008d584f0 ffffffc976b57080 [ 4.464846] fcc0: ffffffc976af38d0 ffffffc975c20168 ffffffc975dafd10 ffffff800850d338 [ 4.472630] fce0: ffffffc976b57020 ffffffc976b57020 ffffff8008d584f0 ffffff8008d3d000 [ 4.480414] fd00: ffffffc976b57020 0000000000000001 ffffffc975dafd20 ffffff800850c124 [ 4.488198] fd20: ffffffc975dafd50 ffffff800850c5b0 ffffffc976b57020 ffffff8008d3d848 [ 4.495982] fd40: ffffff8008d3d820 ffffff800850c5a8 ffffffc975dafd80 ffffff80080d2998 [ 4.503765] fd60: 0000000000000000 ffffffc976bd4500 ffffff8008d3d880 0000000000000000 [ 4.511549] fd80: ffffffc975dafdc0 ffffff80080d2c40 ffffffc976bd4500 ffffffc976815000 [ 4.519333] fda0: ffffffc976bd4530 ffffffc976815020 ffffff8008ce5000 ffffffc975dac000 [ 4.527117] fdc0: ffffffc975dafe20 ffffff80080d8918 ffffffc976bd3880 ffffff8008d9cb08 [ 4.534900] fde0: ffffff8008ace5f0 ffffffc976bd4500 ffffff80080d2bf8 0000000000000000 [ 4.542683] fe00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.550467] fe20: 0000000000000000 ffffff8008082e90 ffffff80080d8848 ffffffc976bd3880 [ 4.558250] fe40: 0000000000000000 0000000000000000 0000000000000000 0000d00420000400 [ 4.566034] fe60: ffffffc975dafea0 0000000000000000 ffffff80080d8848 ffffffc976bd4500 [ 4.573817] fe80: 0000000000000000 0000000000000000 ffffffc975dafe90 ffffffc975dafe90 [ 4.581602] fea0: 0000000000000000 ffffff8000000000 ffffffc975dafeb0 ffffffc975dafeb0 [ 4.589384] fec0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.597168] fee0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.604951] ff00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.612734] ff20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.620517] ff40: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.628299] ff60: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.636082] ff80: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.643865] ffa0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4.651648] ffc0: 0000000000000000 0000000000000005 0000000000000000 0000000000000000 [ 4.659431] ffe0: 0000000000000000 0000000000000000 100a0c0062800800 42200c0000000c00 [ 4.667210] Call trace: [ 4.669643] Exception stack(0xffffffc975daf840 to 0xffffffc975daf970) [ 4.676040] f840: ffffffc976bf9018 0000008000000000 ffffffc975dafa10 ffffff80084c46f0 [ 4.683823] f860: 0000000000000000 0000000000000000 00000001800f000e 0000000000000001 [ 4.691607] f880: ffffffc9769ef2a0 00000001000f000f ffffffbf25da7a00 ffffffc976803100 [ 4.699390] f8a0: ffffffc975daf9b0 ffffff80081a899c ffffffc976803100 ffffff80083446b4 [ 4.707174] f8c0: ffffffbf25da7a00 ffffffc975dac000 ffffffc9769ef2a0 000000000003c380 [ 4.714958] f8e0: 0000000000000000 0000000000000000 ffffffc975df3800 ffffff8008504128 [ 4.722741] f900: 0000000000000080 ffffff80084b7b8c 000000000000001b ffffffc97fea8c00 [ 4.730524] f920: 0000000000210d00 0000000040000000 0000000000000000 0101010101010101 [ 4.738308] f940: 0000000000000038 ffffffc97681e185 ffffffffffffffff ffffffc97681e91c [ 4.746090] f960: 000000008ff5d35f 0000000074ce71ee [ 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 ]---
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().
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.
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?
Robin.
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:
----->8----- From: Robin Murphy robin.murphy@arm.com 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@armlinux.org.uk Signed-off-by: Robin Murphy robin.murphy@arm.com --- 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);
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@arm.com 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@armlinux.org.uk Signed-off-by: Robin Murphy robin.murphy@arm.com
Acked-by: Liviu Dudau Liviu.Dudau@arm.com
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
dri-devel@lists.freedesktop.org
-
Liviu Dudau -
Robin Murphy -
Russell King - ARM Linux