linux-hardening - Re: [RFC 1/1] drivers/dma/*: replace tasklets with workqueue

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Date:   Wed, 25 May 2022 19:48:36 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Allen Pais <apais@...ux.microsoft.com>
Cc:     David Laight <David.Laight@...lab.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "olivier.dautricourt@...lia.com" <olivier.dautricourt@...lia.com>,
        Stefan Roese <sr@...x.de>, Vinod Koul <vkoul@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Paul Cercueil <paul@...pouillou.net>,
        "Eugeniy.Paltsev@...opsys.com" <Eugeniy.Paltsev@...opsys.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Leo Li <leoyang.li@....com>,
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        Haojian Zhuang <haojian.zhuang@...il.com>,
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        Patrice CHOTARD <patrice.chotard@...s.st.com>,
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        Jernej Škrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 1/1] drivers/dma/*: replace tasklets with workqueue

On Wed, May 25, 2022 at 6:56 PM Allen Pais <apais@...ux.microsoft.com> wrote:
>
> Thank you Linus, Arnd, Vincent and David for the feedback.
>
> This is a lot more than a just conversion of API’s. I am in the process
> Of replacing tasklets with threaded irq’s and hopefully that should be
> A better solution than using workqueues.

I don't think that is much better for the case of the DMA engine
callbacks than the work queue, the problem I pointed out here
is scheduling into task context, which may be too expensive
in some cases, but whether it is or not depends on the slave
driver, not the dmaengine driver.

Even if all the slave drivers are better off using task context
(threaded irq or workqueue), you need to look at the slave
drivers first before you can convert the dmaengine drivers.

        Arnd