linux-kernel - Re: Problem with VMAP

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Message-ID: <CALCETrVWYfijXeuKzk6FDDReaKXXP6Wck=80wtTohS8JpJND6A@mail.gmail.com>
Date:   Wed, 5 Oct 2016 08:53:11 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Jörg Otte <jrg.otte@...il.com>
Cc:     Mauro Carvalho Chehab <mchehab@...pensource.com>,
        Jiri Kosina <jikos@...nel.org>,
        Patrick Boettcher <patrick.boettcher@...teo.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Michael Krufky <mkrufky@...uxtv.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: Problem with VMAP_STACK=y

On Wed, Oct 5, 2016 at 8:21 AM, Jörg Otte <jrg.otte@...il.com> wrote:
> 2016-10-05 11:04 GMT+02:00 Mauro Carvalho Chehab <mchehab@...pensource.com>:
>> Em Wed, 5 Oct 2016 09:50:42 +0200 (CEST)
>> Jiri Kosina <jikos@...nel.org> escreveu:
>>
>>> On Wed, 5 Oct 2016, Patrick Boettcher wrote:
>>>
>>> > > > Thanks for the quick response.
>>> > > > Drivers are:
>>> > > > dvb_core, dvb_usb, dbv_usb_cynergyT2
>>> > >
>>> > > This dbv_usb_cynergyT2 is not from Linus' tree, is it? I don't seem
>>> > > to be able to find it, and the only google hit I am getting is your
>>> > > very mail to LKML :)
>>> >
>>> > It's a typo, it should say dvb_usb_cinergyT2.
>>>
>>> Ah, thanks. Same issues there in
>>>
>>>       cinergyt2_frontend_attach()
>>>       cinergyt2_rc_query()
>>>
>>> I think this would require more in-depth review of all the media drivers
>>> and having all this fixed for 4.9. It should be pretty straightforward;
>>> all the instances I've seen so far should be just straightforward
>>> conversion to kmalloc() + kfree(), as the buffer is not being embedded in
>>> any structure etc.
>>
>> What we're doing on most cases is to put a buffer (usually with 80
>> chars for USB drivers) inside the "state" struct (on DVB drivers),
>> in order to avoid doing kmalloc/kfree all the times. One such patch is
>> changeset c4a98793a63c4.
>>
>> I'm enclosing a non-tested patch fixing it for the cinergyT2-core.c
>> driver.
>>
>> Thanks,
>> Mauro
>>
>> [PATCH] cinergyT2-core: don't do DMA on stack
>>
>
> Tried the cinergyT2 patch. No success. When I select a TV channel
> just nothing happens. There are no error messages.

Could you try compiling with CONFIG_DEBUG_VIRTUAL=y and seeing if you
get a nice error message?

--Andy