Re: [RFC][PATCH 5/7] kref: Implement kref_put_lock()

[Peter Zijlstra]

On Mon, Nov 14, 2016 at 12:35:48PM -0800, Kees Cook wrote:
> On Mon, Nov 14, 2016 at 9:39 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > Because home-rolling your own is _awesome_, stop doing it. Provide
> > kref_put_lock(), just like kref_put_mutex() but for a spinlock.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > ---
> >  include/linux/kref.h |   21 +++++++++++++++------
> >  net/sunrpc/svcauth.c |   15 ++++++++++-----
> >  2 files changed, 25 insertions(+), 11 deletions(-)
> >
> > --- a/include/linux/kref.h
> > +++ b/include/linux/kref.h
> > @@ -86,12 +86,21 @@ static inline int kref_put_mutex(struct
> >                                  struct mutex *lock)
> >  {
> >         WARN_ON(release == NULL);
> 
> This WARN_ON makes sense, yes, though it seems like it should be deal
> with differently. If it's NULL, we'll just Oops when we call release()
> later... Seems like this should saturate the kref or something else
> similar.

So I simply took the pattern from the existing kref_put().

But I like it more in these kref_put_{lock,mutex}() variants, because
someone will need to unlock. If we simply crash/bug without unlock we'll
have broken state the rest of the kernel cannot fix up.