Re: [PATCH] TW686x: Fix OOPS on buffer alloc failure

[khalasa@piap.pl (Krzysztof Hałasa)]

Ezequiel Garcia <ezequiel@vanguardiasur.com.ar> writes:

>> +       /* Initialize vc->dev and vc->ch for the error path first */
>> +       for (ch = 0; ch < max_channels(dev); ch++) {
>> +               struct tw686x_video_channel *vc = &dev->video_channels[ch];
>> +               vc->dev = dev;
>> +               vc->ch = ch;
>> +       }
>> +
>
> I'm not sure where is the oops this commit fixes, care to explain it to me?

The error path apparently calls tw686x_video_free() which requires
vc->dev to be initialized. Now, the vc->dev is set for the channel being
currently initialized (unsuccesfully), but not for ones which haven't
been initialized yet. tw686x_video_free() iterates over the whole set.

It seems it also happens in "memcpy" mode. I didn't test it before since
on my ARMv7 "memcpy" mode is unusable, it's way too slow. Also, does the
driver attempt to use consistent memory for entire buffers in this mode?
This may work on i686/x86_64 because the caches are coherent by design
and there is no difference between consistent and non-consistent RAM
(if one isn't using SWIOTLB etc).

tw6869: PCI 0000:07:00.0, IRQ 24, MMIO 0x1100000 (memcpy mode)
tw686x 0000:07:00.0: enabling device (0140 -> 0142)
tw686x 0000:07:00.0: dma0: unable to allocate P-buffer
Unable to handle kernel NULL pointer dereference at virtual address 00000000
PC is at _raw_spin_lock_irqsave+0x10/0x4c
LR is at tw686x_memcpy_dma_free+0x1c/0x124
pc : [<805a8b14>]    lr : [<7f04a3c0>]    psr: 20010093
sp : be915c80  ip : 00000000  fp : bea1b000
r10: 00000000  r9 : fffffff4  r8 : 0000b000
r7 : 00000000  r6 : 000003f0  r5 : 00000000  r4 : bf0e21f8
r3 : 7f04a3a4  r2 : 00000000  r1 : 00000000  r0 : 20010013
Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 4e91804a  DAC: 00000051
Process udevd (pid: 88, stack limit = 0xbe914210)
(_raw_spin_lock_irqsave) from (tw686x_memcpy_dma_free+0x1c/0x124)
(tw686x_memcpy_dma_free) from (tw686x_video_free+0x50/0x78)
(tw686x_video_free) from (tw686x_video_init+0x478/0x5e8)
(tw686x_video_init) from (tw686x_probe+0x36c/0x3fc)
(tw686x_probe) from (pci_device_probe+0x88/0xf4)
(pci_device_probe) from (driver_probe_device+0x238/0x2d8)
(driver_probe_device) from (__driver_attach+0xac/0xb0)
(__driver_attach) from (bus_for_each_dev+0x6c/0xa0)
(bus_for_each_dev) from (bus_add_driver+0x1a0/0x218)
(bus_add_driver) from (driver_register+0x78/0xf8)
(driver_register) from (do_one_initcall+0x40/0x168)
(do_one_initcall) from (do_init_module+0x60/0x3a4)
(do_init_module) from (load_module+0x1c90/0x20e4)
(load_module) from (SyS_finit_module+0x8c/0x9c)
(SyS_finit_module) from (ret_fast_syscall+0x0/0x3c)
Code: e1a02000 e10f0000 f10c0080 f592f000 (e1923f9f)


With the patch:
tw6869: PCI 0000:07:00.0, IRQ 24, MMIO 0x1100000 (memcpy mode)
tw686x 0000:07:00.0: enabling device (0140 -> 0142)
tw686x 0000:07:00.0: dma0: unable to allocate P-buffer
tw686x 0000:07:00.0: can't register video
tw686x: probe of 0000:07:00.0 failed with error -12
--
Krzysztof Halasa

Industrial Research Institute for Automation and Measurements PIAP
Al. Jerozolimskie 202, 02-486 Warsaw, Poland