linux-kernel - RE: [PATCH 14/15] kernel: convert futex_pi_state.refcount from atomic_t to refcount

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Date:   Fri, 7 Jul 2017 10:24:20 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-audit@...hat.com" <linux-audit@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "tj@...nel.org" <tj@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "lizefan@...wei.com" <lizefan@...wei.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "eparis@...hat.com" <eparis@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "luto@...nel.org" <luto@...nel.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH 14/15] kernel: convert futex_pi_state.refcount from
 atomic_t to refcount_t

> On Fri, Jul 07, 2017 at 12:04:28PM +0300, Elena Reshetova wrote:
> > refcount_t type and corresponding API should be
> > used instead of atomic_t when the variable is used as
> > a reference counter. This allows to avoid accidental
> > refcounter overflows that might lead to use-after-free
> > situations.
> >
> > Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> > Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Signed-off-by: David Windsor <dwindsor@...il.com>
> 
> I'll let tglx comment on the SoB chain, I know he likes those :-) You
> did Cc him right, seeing how he's the maintainer of this stuff..
> 
> *sigh* you didn't :-( After so many patches send you _really_ should
> know to Cc the right people.

It is not so trivial as you might think. Unless right  person shows up as maintainer/supporter
when I run get_maintainer script, it is hard to figure out who is the right CC person. 
And the amount of sending patches doesn't help, because if a person reacts on
patches and asks to change/fix stuff, it doesn't mean he is the right person, 
he might be just reading mailing list and having time to do reviews :(

That's said, I will try to improve the CC list. 


> 
> > ---
> >  kernel/futex.c | 13 +++++++------
> >  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> > @@ -814,7 +815,7 @@ static struct futex_pi_state *alloc_pi_state(void)
> >
> >  static void get_pi_state(struct futex_pi_state *pi_state)
> >  {
> > -	WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
> > +	WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
> >  }
> 
> I think we have refcount_inc() for just that case, no?
> 

Yes, this slipped through. Will fix so it would look shorted.  Thank you for catching it!

Best Regards,
Elena.