netdev - Re: [patch V2 08/15] Documentation: Add lock ordering and nesting documentation

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Message-ID: <20200322013624.GA161885@google.com>
Date:   Sat, 21 Mar 2020 21:36:24 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Logan Gunthorpe <logang@...tatee.com>,
        Kurt Schwemmer <kurt.schwemmer@...rosemi.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.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,
        Oleg Nesterov <oleg@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arnd Bergmann <arnd@...db.de>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [patch V2 08/15] Documentation: Add lock ordering and nesting
 documentation

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