From: Kees Cook <keescook@chromium.org>
To: peterz@infradead.org
Cc: David Howells <dhowells@redhat.com>,
Xiaoming Ni <nixiaoming@huawei.com>,
David Windsor <dwindsor@gmail.com>,
Hans Liljestrand <ishkamiel@gmail.com>,
Elena Reshetova <elena.reshetova@intel.com>,
Paul Moore <paul@paul-moore.com>,
edumazet@google.com, paulmck@kernel.org, shakeelb@google.com,
James Morris <jamorris@linux.microsoft.com>,
alex.huangjianhui@huawei.com, dylix.dailei@huawei.com,
chenzefeng2@huawei.com, linux-kernel@vger.kernel.org,
Will Deacon <will@kernel.org>
Subject: Re: [RFC][PATCH] locking/refcount: Provide __refcount API to obtain the old value
Date: Wed, 29 Jul 2020 12:29:14 -0700 [thread overview]
Message-ID: <202007291228.5DFF9315@keescook> (raw)
In-Reply-To: <20200729113731.GA2678@hirez.programming.kicks-ass.net>
On Wed, Jul 29, 2020 at 01:37:31PM +0200, peterz@infradead.org wrote:
> On Wed, Jul 29, 2020 at 01:11:20PM +0200, peterz@infradead.org wrote:
>
> > Subject: locking/refcount: Provide __refcount API to obtain the old value
> > From: Peter Zijlstra <peterz@infradead.org>
> > Date: Wed Jul 29 13:00:57 CEST 2020
> >
> > David requested means to obtain the old/previous value from the
> > refcount API for tracing purposes.
> >
> > Duplicate (most of) the API as __refcount*() with an additional
> > 'int *' argument into which, if !NULL, the old value will be stored.
> >
> > Requested-by: David Howells <dhowells@redhat.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> > include/linux/refcount.h | 65 +++++++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 57 insertions(+), 8 deletions(-)
> >
> > --- a/include/linux/refcount.h
> > +++ b/include/linux/refcount.h
> > @@ -165,7 +165,7 @@ static inline unsigned int refcount_read
> > *
> > * Return: false if the passed refcount is 0, true otherwise
> > */
> > -static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)
> > +static inline __must_check bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp)
> > {
> > int old = refcount_read(r);
> >
> > @@ -174,12 +174,20 @@ static inline __must_check bool refcount
> > break;
> > } while (!atomic_try_cmpxchg_relaxed(&r->refs, &old, old + i));
> >
> > + if (oldp)
> > + *oldp = old;
> > +
> > if (unlikely(old < 0 || old + i < 0))
> > refcount_warn_saturate(r, REFCOUNT_ADD_NOT_ZERO_OVF);
> >
> > return old;
> > }
> >
> > +static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)
> > +{
> > + return __refcount_add_not_zero(i, r, NULL);
> > +}
>
> so, I could also emulate C++'s
>
> bool refcount_add_not_zero(int i, refcount_t *r, int *oldp = NULL)
>
> style by going to town on this with a bunch of CPP magic, but I don't
> think that'll actually make things clearer.
Erg. No, I like the __-version better -- it looks more like other kernel
APIs.
--
Kees Cook
next prev parent reply other threads:[~2020-07-29 19:29 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-12 18:34 [PATCH 0/3] Convert nsproxy, groups, and creds to refcount_t Kees Cook
2020-06-12 18:34 ` [PATCH 1/3] nsproxy: convert nsproxy.count " Kees Cook
2020-06-12 18:34 ` [PATCH 2/3] groups: convert group_info.usage " Kees Cook
2020-06-15 0:57 ` [groups] 67467ae141: will-it-scale.per_process_ops 4.3% improvement kernel test robot
2020-06-12 18:34 ` [PATCH 3/3] creds: convert cred.usage to refcount_t Kees Cook
2020-06-15 2:02 ` Xiaoming Ni
2020-06-15 2:10 ` [PATCH 0/3] Convert nsproxy, groups, and creds " Xiaoming Ni
2020-06-15 3:55 ` Kees Cook
2020-06-15 5:35 ` Reshetova, Elena
2020-06-15 18:08 ` Kees Cook
2020-06-18 7:39 ` Reshetova, Elena
2020-07-21 11:02 ` David Howells
2020-07-21 10:51 ` David Howells
2020-07-21 18:44 ` Kees Cook
2020-07-21 19:51 ` Peter Zijlstra
2020-07-28 10:56 ` David Howells
2020-07-29 11:11 ` [RFC][PATCH] locking/refcount: Provide __refcount API to obtain the old value peterz
2020-07-29 11:37 ` peterz
2020-07-29 19:29 ` Kees Cook [this message]
2020-07-29 19:30 ` Kees Cook
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-09-21 11:22 ` [RFC][PATCH] " Will Deacon
2021-01-26 11:25 ` David Howells
2020-07-29 20:41 ` David Howells
2020-07-29 20:52 ` Kees Cook
2020-07-28 11:01 ` [PATCH 0/3] Convert nsproxy, groups, and creds to refcount_t David Howells
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