linux-kernel - Re: [PATCH v2 1/2] spi: spidev: fix a race condition when accessing spidev->spi

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Message-ID: <CAMRc=MejZsbL=Ef=hNV-QGcrcgCepKfnAU4z+CFXFf8Wn09M-g@mail.gmail.com>
Date:   Fri, 6 Jan 2023 17:27:34 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 1/2] spi: spidev: fix a race condition when accessing spidev->spi

On Fri, Jan 6, 2023 at 5:16 PM Mark Brown <broonie@...nel.org> wrote:
>
> On Fri, Jan 06, 2023 at 03:27:57PM +0100, Bartosz Golaszewski wrote:
>
> > IMO the complication of using an RW semaphore is insignificant and
> > maybe a comment next to its declaration in struct spidev would
> > suffice?
>
> The complication is using a semaphore at all, it's a pretty unusual
> locking construct and the whole up/down thing isn't clear to people
> who aren't familiar with it.  Given that there's no clounting being
> used rwlock would be a much more obvious choice if the microseconds
> of extra concurrency is meaningful somehow.

I don't have any numbers, it's just that in this case the rwsem feels
more correct. My opinion is not very strong so you can apply v2.

Bart