From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>,
corbet@lwn.net, gregkh@linuxfoundation.org, shuah@kernel.org,
rafael@kernel.org, johannes@sipsolutions.net, lenb@kernel.org,
james.morse@arm.com, tony.luck@intel.com, bp@alien8.de,
arve@android.com, tkjos@android.com, maco@android.com,
joel@joelfernandes.org, christian@brauner.io, hridya@google.com,
surenb@google.com, minyard@acm.org, arnd@arndb.de,
mchehab@kernel.org, rric@kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-acpi@vger.kernel.org, devel@driverdev.osuosl.org,
openipmi-developer@lists.sourceforge.net,
linux-edac@vger.kernel.org, Will Deacon <will@kernel.org>
Subject: Re: [PATCH v3 00/11] Introduce Simple atomic counters
Date: Sat, 10 Oct 2020 13:09:20 +0200 [thread overview]
Message-ID: <20201010110920.GQ2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <202010091255.246395A6@keescook>
On Fri, Oct 09, 2020 at 01:45:43PM -0700, Kees Cook wrote:
> On Fri, Oct 09, 2020 at 09:37:46PM +0200, Peter Zijlstra wrote:
> > On Fri, Oct 09, 2020 at 09:55:55AM -0600, Shuah Khan wrote:
> > > Simple atomic counters api provides interfaces for simple atomic counters
> > > that just count, and don't guard resource lifetimes. The interfaces are
> > > built on top of atomic_t api, providing a smaller subset of atomic_t
> > > interfaces necessary to support simple counters.
> >
> > To what actual purpose?!? AFACIT its pointless wrappery, it gets us
> > nothing.
>
> It's not pointless. There is value is separating types for behavioral
> constraint to avoid flaws. atomic_t provides a native operation. We gained
> refcount_t for the "must not wrap" type, and this gets us the other side
> of that behavioral type, which is "wrapping is expected". Separating the
> atomic_t uses allows for a clearer path to being able to reason about
> code flow, whether it be a human or a static analyzer.
refcount_t got us actual rutime exceptions that atomic_t doesn't. This
propsal gets us nothing.
atomic_t is very much expected to wrap.
> The counter wrappers add nothing to the image size, and only serve to
> confine the API to one that cannot be used for lifetime management.
It doesn't add anything period. It doesn't get us new behaviour, it
splits a 'can wrap' use-case from a 'can wrap' type. That's sodding
pointless.
Worse, it mixes 2 unrelated cases into one type, which just makes a
mockery of things (all the inc_return users are not statistics, some
might even mis-behave if they wrap).
> Once conversions are done, we have a clean line between refcounting
> and statistical atomics, which means we have a much lower chance of
> introducing new flaws (and maybe we'll fix flaws during the conversion,
> which we've certainly seen before when doing this stricter type/language
> changes).
>
> I don't see why this is an objectionable goal.
People can and will always find a way to mess things up.
Only add types when you get behavioural changes, otherwise it's
pointless noise.
My NAK stands.
next prev parent reply other threads:[~2020-10-10 23:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-09 15:55 [PATCH v3 00/11] Introduce Simple atomic counters Shuah Khan
2020-10-09 15:56 ` [PATCH v3 11/11] drivers/edac: convert pci counters to counter_atomic32 Shuah Khan
2020-10-09 18:03 ` [PATCH v3 00/11] Introduce Simple atomic counters Kees Cook
2020-10-09 19:02 ` Shuah Khan
2020-10-09 19:37 ` Peter Zijlstra
2020-10-09 20:45 ` Kees Cook
2020-10-10 11:09 ` Peter Zijlstra [this message]
2020-10-14 2:12 ` Shuah Khan
2020-10-14 9:17 ` Peter Zijlstra
2020-10-14 23:31 ` Kees Cook
2020-10-16 10:53 ` Peter Zijlstra
2020-10-16 22:51 ` Kees Cook
2020-11-10 18:49 ` Dan Carpenter
2020-10-16 21:56 ` Shuah Khan
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