linux-kernel - Re: Documentation/locking/locktypes: Further clarifications and wordsmithing

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Date:   Wed, 25 Mar 2020 17:02:12 +0100
From:   Sebastian Siewior <bigeasy@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     paulmck@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kurt Schwemmer <kurt.schwemmer@...rosemi.com>,
        linux-pci@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>, linux-usb@...r.kernel.org,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        platform-driver-x86@...r.kernel.org,
        Zhang Rui <rui.zhang@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-pm@...r.kernel.org, Len Brown <lenb@...nel.org>,
        linux-acpi@...r.kernel.org, kbuild test robot <lkp@...el.com>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Guo Ren <guoren@...nel.org>, linux-csky@...r.kernel.org,
        Brian Cain <bcain@...eaurora.org>,
        linux-hexagon@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org,
        Michal Simek <monstr@...str.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arnd Bergmann <arnd@...db.de>,
        Geoff Levand <geoff@...radead.org>,
        linuxppc-dev@...ts.ozlabs.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: Documentation/locking/locktypes: Further clarifications and
 wordsmithing

On 2020-03-25 13:27:49 [+0100], Thomas Gleixner wrote:
> The documentation of rw_semaphores is wrong as it claims that the non-owner
> reader release is not supported by RT. That's just history biased memory
> distortion.
> 
> Split the 'Owner semantics' section up and add separate sections for
> semaphore and rw_semaphore to reflect reality.
> 
> Aside of that the following updates are done:
> 
>  - Add pseudo code to document the spinlock state preserving mechanism on
>    PREEMPT_RT
> 
>  - Wordsmith the bitspinlock and lock nesting sections
> 
> Co-developed-by: Paul McKenney <paulmck@...nel.org>
> Signed-off-by: Paul McKenney <paulmck@...nel.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

> --- a/Documentation/locking/locktypes.rst
> +++ b/Documentation/locking/locktypes.rst
…
> +rw_semaphore
> +============
> +
> +rw_semaphore is a multiple readers and single writer lock mechanism.
> +
> +On non-PREEMPT_RT kernels the implementation is fair, thus preventing
> +writer starvation.
> +
> +rw_semaphore complies by default with the strict owner semantics, but there
> +exist special-purpose interfaces that allow non-owner release for readers.
> +These work independent of the kernel configuration.

This reads funny, could be my English. "This works independent …" maybe?

Sebastian