Re: [PATCH 4.19 28/37] dmaengine: dmatest: Fix iteration non-stop logic

From: Pavel Machek <pavel@denx.de>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Pavel Machek <pavel@denx.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Stable <stable@vger.kernel.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Nicolas Ferre <nicolas.ferre@microchip.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Vinod Koul <vkoul@kernel.org>
Subject: Re: [PATCH 4.19 28/37] dmaengine: dmatest: Fix iteration non-stop logic
Date: Tue, 5 May 2020 16:53:18 +0200	[thread overview]
Message-ID: <20200505145317.GA2834@amd> (raw)
In-Reply-To: <CAHp75Ve+pzhamZXiKxHF+VD8yfsjRF2coattHyiD+0aa7Fy2DA@mail.gmail.com>

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On Tue 2020-05-05 17:05:37, Andy Shevchenko wrote:
> On Tue, May 5, 2020 at 4:37 PM Pavel Machek <pavel@denx.de> wrote:
> > On Tue 2020-05-05 16:19:11, Andy Shevchenko wrote:
> > > On Tue, May 5, 2020 at 3:58 PM Pavel Machek <pavel@denx.de> wrote:
> > > > On Tue 2020-05-05 15:51:16, Andy Shevchenko wrote:
> > > > > On Tue, May 5, 2020 at 3:37 PM Pavel Machek <pavel@denx.de> wrote:
> > > > > > > So, to the point, the conditional of checking the thread to be stopped being
> > > > > > > first part of conjunction logic prevents to check iterations. Thus, we have to
> > > > > > > always check both conditions
> 
> vvv
> >>>>>> to be able to stop after given iterations.
> ^^^

_If_ you are already stopping due to kthread_should_stop(), you don't
need to check iterations.

If you are not stopping, iterations are always checked.

No, the new code does not "always check both conditions" as you claim.

> Yes. Please, read carefully the commit message (for your convenience I
> emphasized above). I don't want to spend time on this basics stuff
> anymore.

You may want to go through the basics once more. The change clearly
does not do what you said it does; in fact, it does not do anything.

> > If you wanted both conditions to always evaluate, you'd have to do
> >
> > #       while (!kthread_should_stop()
> > #              & !(params->iterations && total_tests >=
> > #              params->iterations)) {
> >
> > (note && -> &). But, again, there's no reason to do that, as second
> > part of expression does not have side effects.
> 
> It fixes a bug in the code, try with and without this change. (I can
> reproduce it here)

I'm not sure if you made mistake during testing, or if you have buggy
compiler or what...
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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