Re: [patch 00/13] preempt: Make preempt count unconditional

Paul E. McKenney
2020-09-16T20:44:05Z

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