linux-kernel - Re: [PATCH v1 3/7] dmaengine: tegra-apb: Prevent race conditions on channel's freeing

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Message-ID: <20191230205054.GC24135@qmqm.qmqm.pl>
Date:   Mon, 30 Dec 2019 21:50:54 +0100
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Laxman Dewangan <ldewangan@...dia.com>,
        Vinod Koul <vkoul@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        dmaengine@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/7] dmaengine: tegra-apb: Prevent race conditions on
 channel's freeing

On Mon, Dec 30, 2019 at 09:45:55PM +0100, Michał Mirosław wrote:
> On Sat, Dec 28, 2019 at 11:46:36PM +0300, Dmitry Osipenko wrote:
> > It's unsafe to check the channel's "busy" state without taking a lock,
> > it is also unsafe to assume that tasklet isn't in-fly.
> 
> 'in-flight'. Also, the patch seems to have two independent bug-fixes
> in it. Second one doesn't look right, at least not without an explanation.
> 
> First:
> 
> > -	if (tdc->busy)
> > -		tegra_dma_terminate_all(dc);
> > +	tegra_dma_terminate_all(dc);
> 
> Second:
> 
> > +	tasklet_kill(&tdc->tasklet);

BTW, maybe you can convert the code to threaded interrupt handler and
just get rid of the tasklet instead of fixing it?

Best Regards,
Michał Mirosław