linux-kernel - Re: [RFC][PATCH 7/7] kref: Implement using refcount

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Date:   Tue, 15 Nov 2016 11:03:59 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     gregkh@...uxfoundation.org, keescook@...omium.org,
        will.deacon@....com, elena.reshetova@...el.com, arnd@...db.de,
        tglx@...utronix.de, hpa@...or.com, dave@...gbits.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 7/7] kref: Implement using refcount_t


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Nov 15, 2016 at 09:40:09AM +0100, Ingo Molnar wrote:
> > 
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > Provide refcount_t, an atomic_t like primitive built just for
> > > refcounting.
> > > 
> > > It provides overflow and underflow checks as well as saturation
> > > semantics such that when it overflows, we'll never attempt to free it
> > > again, ever.
> > > 
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > > ---
> > >  include/linux/kref.h     |   29 ++----
> > >  include/linux/refcount.h |  221 +++++++++++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 232 insertions(+), 18 deletions(-)
> > 
> > I'd suggest splitting this patch into two parts: first patch introduces the 
> > refcount.h facility, second patch changes over struct kref to the new facility.
> 
> You're right, I was just really glad I got it to compile and didn't want
> to prod more at it.
>
> Should I also make a CONFIG knob that implements refcount_t with the
> 'normal' atomic_t primitives?

I'd suggest doing the saturation/safe-wrap semantics only for now (i.e. the 
current patch, split into two perhaps), and reconsider if there's any complaints?

> And possibly another knob to toggle the BUG()s into WARN()s. With the
> full saturation semantics WARN() is a lot safer and will not corrupt
> kernel state as much.

I'd suggest changing it to a WARN() straight away, no extra knobs.

Thanks,

	Ingo