Re: 4.6-rc3 hung at tty_port_block_til_ready+0x11c/0x2a0

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2016-04-19 6:01 GMT+03:00 Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>:
> On 04/18/2016 07:18 AM, Matwey V. Kornilov wrote:
>> 2016-04-18 9:55 GMT+03:00 Jiri Slaby <jslaby@xxxxxxx>:
>>> On 04/17/2016, 02:33 PM, Matwey V. Kornilov wrote:
>>>> Hello,
>>>>
>>>> When running 4.6-rc3 (please find used config attached) on BeagleBone Black with 8250_omap serial driver I see the following hung.
>

Hello,

> What uart # (0-5) are you using?

I am using uart5 (ttyS5).

> Are you using not-yet-mainline patches to 8250 driver (like for gpio modem control)?

No, I use vanilla 4.6-rc3 (and 4.5 behaviour is the same).

>
>
>>>> When test application a.out run twice (test.c source code attached here) the following happens:
>>>>
>>>> # ./a.out # ./a.out
>>>> (hung here, may be interrupted with Ctrl-C)
>>>>
>>>> Trace from echo t > /proc/sysrq-trigger is the following:
>>>>
>>>> апр 17 12:29:23 nohostname kernel: a.out           S c0c3544c     0   922    882 0x00000000
>>>> апр 17 12:29:23 nohostname kernel: [<c0c3544c>] (__schedule) from [<c0c3597c>] (schedule+0x5c/0xd0)
>>>> апр 17 12:29:23 nohostname kernel: [<c0c3597c>] (schedule) from [<c0794820>] (tty_port_block_til_ready+0x11c/0x2a0)
>>>> апр 17 12:29:23 nohostname kernel: [<c0794820>] (tty_port_block_til_ready) from [<c07abfb0>] (uart_open+0x11c/0x158)
>>> ...
>>>>
>>>> I don't think that open() user-space call should be blocked under such circumstances, so I think that this is rather an issue within the kernel.
>>>> I've found that the effect dissapears when termios calls are dropped from test.c
>
> Assuming you are _not_ using gpio modem control, this shouldn't happen
> because the driver should report TIOCM_CAR always on if DCD is not
> pinned out for exactly this reason.

As Jiri said, CLOCAL prevents open() from blocking. However, my uart
doesn't have any modem control pins in device tree only rts/cts.

>
> IOW, could be driver bug.
>
> Regards,
> Peter Hurley
>
>
>>> I suppose the memset in the program cleared CLOCAL and the subsequent
>>> open waits for carrier...
>>>
>>
>> The same program doesn't hang when fdti_sio based /dev/ttyUSB is being used.
>>
>>> thanks,
>>> --
>>> js
>>> suse labs
>>>
>>
>>
>>
>



-- 
With best regards,
Matwey V. Kornilov.
Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia
119991, Moscow, Universitetsky pr-k 13, +7 (495) 9392382
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