linux-kernel - Re: Bug in add_dma_entry()'s debugging code

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Message-ID: <CAHp75VeQoOFQ7V7gbVfR3-ANNMRT=-UniOCbnUtszo-1F3NMDA@mail.gmail.com>
Date:   Tue, 28 Nov 2023 18:34:39 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Christoph Hellwig <hch@....de>,
        Hamza Mahfooz <someguy@...ective-light.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Andrew <travneff@...il.com>,
        Ferry Toth <ferry.toth@...inga.info>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        iommu@...ts.linux.dev,
        Kernel development list <linux-kernel@...r.kernel.org>,
        USB mailing list <linux-usb@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: Bug in add_dma_entry()'s debugging code

On Tue, Nov 28, 2023 at 6:31 PM Robin Murphy <robin.murphy@....com> wrote:
> On 28/11/2023 3:18 pm, Alan Stern wrote:
> > On Tue, Nov 28, 2023 at 02:37:02PM +0100, Christoph Hellwig wrote:

...

> >> The logical confcusion from that would be that IFF dma-debug is enabled on
> >> any platform we need to set ARCH_DMA_MINALIGN to the cache line size.
> >
> > (IF, not IFF.)  And tell distributions that CONFIG_DMA_API_DEBUG is not
> > meant for production systems but rather for kernel testing, right?
>
> Yikes, I'd hope that distros are heeding the warning that the Kconfig
> calls out already. It's perhaps somewhat understated, as I'd describe
> the performance impact to large modern systems with high-bandwidth I/O
> as somewhere between "severe" and "crippling".

Independently on the distros configurations the (false positive)
message(s) will make difficult to debug the actual things, shouldn't
we have our code robust in any case?

-- 
With Best Regards,
Andy Shevchenko