Re: [PATCH 1/2] dmaengine: usb-dmac: Fix crash on runtime suspend

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 10/2/2015 4:00 AM, Yoshihiro Shimoda wrote:

>>>> If CONFIG_PREEMPT=y:
>>
>>      Actually, it happens even with CONFIG_PREEMPT_VOLUNTARY=y.
>>
>>>>       Unable to handle kernel NULL pointer dereference at virtual address 00000014
>>>>       pgd = c0003000
>>>>       [00000014] *pgd=80000040004003, *pmd=00000000
>>>>       Internal error: Oops: 206 [#1] PREEMPT SMP ARM
>>>>       Modules linked in:
>>>>       CPU: 0 PID: 17 Comm: kworker/0:1 Tainted: G        W       4.3.0-rc3-koelsch-022
>>>>       71-g705498fc5e6a5da8-dirty #1789
>>>>       Hardware name: Generic R8A7791 (Flattened Device Tree)
>>>>       Workqueue: pm pm_runtime_work
>>>>       task: ef578e40 ti: ef57a000 task.ti: ef57a000
>>>>       PC is at usb_dmac_chan_halt+0xc/0xc0
>>>>       LR is at usb_dmac_runtime_suspend+0x28/0x38
>>>>       pc : [<c023c880>]    lr : [<c023c95c>]    psr: 80000113
>>>>       sp : ef57bdf8  ip : 00000008  fp : 00000003
>>>>       r10: 00000008  r9 : c06ab928  r8 : ef49e810
>>>>       r7 : 00000000  r6 : 000000ac  r5 : ef770010  r4 : 00000000
>>>>       r3 : 00000000  r2 : 8ffc2b84  r1 : 00000000  r0 : ef770010
>>>>       Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
>>>>       Control: 30c5307d  Table: 40003000  DAC: fffffffd
>>>>       Process kworker/0:1 (pid: 17, stack limit = 0xef57a210)
>>>>       Stack: (0xef57bdf8 to 0xef57c000)
>>>>
>>>>       [...
>>>>
>>>>       [<c023c880>] (usb_dmac_chan_halt) from [<c023c95c>] (usb_dmac_runtime_suspend+0x28/0x38)
>>>>       [<c023c95c>] (usb_dmac_runtime_suspend) from [<c027b25c>] (pm_genpd_runtime_suspend+0x74/0x23c)
>>>>
>>>> This happens because usb_dmac_probe() calls pm_runtime_put() before
>>>> usb_dmac_chan_probe(), leading to the device being suspended before the
>>>> DMA channels are initialized, causing a NULL pointer dereference.
>>>>
>>>> Move the call to pm_runtime_put() to the end of usb_dmac_probe() to fix
>>>> this.
>>>>
>>>> Add a check to usb_dmac_runtime_suspend() to prevent the crash from
>>>> happening in the error path.
>>>>
>>>> Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
>>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>>>
>>> I could not duplicate this issue completely on Lager.
>>> Even if I enabled ealyprintk, I didn't see the panic log.
>>> (Several kernel message appeared, and then the kernel hung.)
>>
>>      I guess you also need to specify console=. The device tree console
>> assignment (from the "stdout-path" prop) happens too late, the console gets
>> switched to /dev/tty0 first. I forgot to mention that the pseudo-console
>> (CONFIG_VT) should be disabled as well.
>
> Thank you for your comment!
> I was able to look the panic log if I added specify console= in the bootargs.
> (Even if CONFIG_VT=y, the log appeared.)

    Yeah, I got things somewhat mixed up, specifying console= alone should help.

MBR, Sergei