From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: [patch 00/13] preempt: Make preempt count unconditional
Date: Wed, 16 Sep 2020 13:43:59 -0700
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Daniel Vetter <daniel@ffwll.ch>, Thomas Gleixner <tglx@linutronix.de>, Ard Biesheuvel <ardb@kernel.org>, Herbert Xu <herbert@gondor.apana.org.au>, LKML <linux-kernel@vger.kernel.org>, linux-arch <linux-arch@vger.kernel.org>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Valentin Schneider <valentin.schneider@arm.com>, Richard Henderson <rth@twiddle.net>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, alpha <linux-alpha@vger.kernel.org>, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, Anton Ivanov <anton.ivanov@cambridgegreys.com>, linux-um <linux-um@lists.infradead.org>, Brian Cain <bcain@codeaurora.org>, linux-hexagon@vger.kernel.org, Geert Uytterhoeven <geert@linux-m68k.org>, l

On Wed, Sep 16, 2020 at 11:32:00AM -0700, Linus Torvalds wrote:
> On Wed, Sep 16, 2020 at 8:29 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > All fair, but some of us need to write code that must handle being
> > invoked from a wide variety of contexts.
> 
> Note that I think that core functionality is different from random drivers.
> 
> Of course core code can (and will) look at things like
> 
>         if (in_interrupt())
>             .. schedule work asynchronously ..
> 
> because core code ends up being called from odd places, and code like
> that is expected to have understanding of the rules it plays with.
> 
> But something like RCU is a very different beast from some "walk the
> scatter-gather list" code.
> 
> RCU does its work in the background, and works with lots of different
> things. And it's so core and used everywhere that it knows about these
> things. I mean, we literally have special code explicitly to let RCU
> know "we entered kernel context now".
> 
> But something like a driver list walking thing should not be doing
> different things behind peoples back depending on whether they hold
> spinlocks or not. It should either just work regardless, or there
> should be a flag (or special interface) for the "you're being called
> in a crtitical region".
> 
> Because dynamically changing behavior really is very confusing.

Whew!  I feel much better now.  ;-)

							Thanx, Paul