Re: [PATCH] dmatest: abort transfers immediately when asked for

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Vinod Koul <vinod.koul@intel.com>
Cc: Will Deacon <will.deacon@arm.com>,
	Andy Shevchenko <andriy.shevchenko@linux.jf.intel.com>,
	"djbw @ fb . com" <djbw@fb.com>,
	"linux-kernel @ vger . kernel . org"
	<linux-kernel@vger.kernel.org>,
	"linux-arm-kernel @ lists . infradead . org" 
	<linux-arm-kernel@lists.infradead.org>,
	"viresh.kumar@linaro.org" <viresh.kumar@linaro.org>
Subject: Re: [PATCH] dmatest: abort transfers immediately when asked for
Date: Thu, 23 May 2013 13:51:29 +0300	[thread overview]
Message-ID: <CAHp75Vf58kq0t7+et9i54fxjEdQfBrTWxji4xk_MS-fZgWGOdQ@mail.gmail.com> (raw)
In-Reply-To: <20130523100932.GA30200@intel.com>

On Thu, May 23, 2013 at 1:09 PM, Vinod Koul <vinod.koul@intel.com> wrote:
> On Tue, May 21, 2013 at 08:24:15PM +0300, Andy Shevchenko wrote:
>> On Tue, May 21, 2013 at 6:11 PM, Will Deacon <will.deacon@arm.com> wrote:
>> > On Tue, May 21, 2013 at 01:33:17PM +0100, Andy Shevchenko wrote:
>> >> When thread is going to be stopped we have to unconditionally terminate all
>> >> ongoing transfers. Otherwise it would be possible that callback function will
>> >> be called on the next interrupt and will try to access to already freed
>> >> structures.
>> >>
>> >> The patch introduces specific error message for this, though it doesn't
>> >> increase the counter of the failed tests.
>> >>
>> > Thanks for persevering with this! Although this patch definitely fixes the
>> > panic I was seeing, I now observe buffer verification failures in subsequent
>> > test runs after an aborted run:
>>
>> I think the description to the commit adfa543e "dmatest: don't use
>> set_freezable_with_signal()" may shed light on this.
>>
>> The background (if  I got it correctly) is in race with done flag. So,
>> we got a callback call from the DMA engine, but we don't know which
>> transfer triggers it.
>> I might be wrong. This is just an assumption.
>>
>> Have you ever see such behaviour on pre v3.10-rc1 kernels? (I mean
>> with old dmatest module)
> Terminate shouldnt cause the issue with buffer verfication, can you try this on
> dw_dmac, do you see similar failures on verfication?

I saw the similar errors on dw_dmac on Intel Medfield device.
Anyway, I checked another approach with Will.
For now I will send a quick fix that prevents tester to abort an
ongoing transfer.
In future we could implement a robust logic when transfers can be
interrupted at any time.

-- 
With Best Regards,
Andy Shevchenko