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

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Date:   Fri, 6 Jan 2023 17:36:59 +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 5:34 PM Mark Brown <broonie@...nel.org> wrote:
>
> On Fri, Jan 06, 2023 at 05:27:34PM +0100, Bartosz Golaszewski wrote:
> > On Fri, Jan 6, 2023 at 5:16 PM Mark Brown <broonie@...nel.org> wrote:
>
> > > 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.
>
> Like I say the semaphore in particular feels wrong when we don't need
> the counting, we have an explicit reader/writer lock if that's what
> you're trying to accomplish.

Let's go with a mutex and see if anyone complains, if so, we can rethink it.

Bart