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Date:   Sat, 21 Mar 2020 21:36:24 -0400
From:   Joel Fernandes <joel@joelfernandes.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Logan Gunthorpe <logang@deltatee.com>,
        Kurt Schwemmer <kurt.schwemmer@microsemi.com>,
        Bjorn Helgaas <bhelgaas@google.com>, linux-pci@vger.kernel.org,
        Felipe Balbi <balbi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org, Kalle Valo <kvalo@codeaurora.org>,
        "David S. Miller" <davem@davemloft.net>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        Oleg Nesterov <oleg@redhat.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Arnd Bergmann <arnd@arndb.de>, linuxppc-dev@lists.ozlabs.org
Subject: Re: [patch V2 08/15] Documentation: Add lock ordering and nesting
 documentation
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References: <20200318204302.693307984@linutronix.de>
 <20200318204408.211530902@linutronix.de>
 <20200321212144.GA6475@google.com>
 <874kuhqsz3.fsf@nanos.tec.linutronix.de>
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On Sat, Mar 21, 2020 at 10:49:04PM +0100, Thomas Gleixner wrote:
[...] 
> >> +rwsems have grown interfaces which allow non owner release for special
> >> +purposes. This usage is problematic on PREEMPT_RT because PREEMPT_RT
> >> +substitutes all locking primitives except semaphores with RT-mutex based
> >> +implementations to provide priority inheritance for all lock types except
> >> +the truly spinning ones. Priority inheritance on ownerless locks is
> >> +obviously impossible.
> >> +
> >> +For now the rwsem non-owner release excludes code which utilizes it from
> >> +being used on PREEMPT_RT enabled kernels.
> >
> > I could not parse the last sentence here, but I think you meant "For now,
> > PREEMPT_RT enabled kernels disable code that perform a non-owner release of
> > an rwsem". Correct me if I'm wrong.
> 
> Right, that's what I wanted to say :)
> 
> Care to send a delta patch?

Absolutely, doing that now. :-)

thanks,

 - Joel