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From: "Eric W. Biederman" <ebiederm@xmission.com>
To: Kees Cook <keescook@chromium.org>
Cc: Jeff Layton <jlayton@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jann Horn <jannh@google.com>,
	linux-hardening@vger.kernel.org,
	Elena Reshetova <elena.reshetova@intel.com>,
	David Windsor <dwindsor@gmail.com>,
	Hans Liljestrand <ishkamiel@gmail.com>,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	Anna Schumaker <anna@kernel.org>,
	Chuck Lever <chuck.lever@oracle.com>, Neil Brown <neilb@suse.de>,
	Olga Kornievskaia <kolga@netapp.com>,
	Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey <tom@talpey.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Alexey Gladkov <legion@kernel.org>, Yu Zhao <yuzhao@google.com>,
	linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH v2] creds: Convert cred.usage to refcount_t
Date: Fri, 18 Aug 2023 16:07:49 -0500	[thread overview]
Message-ID: <87zg2o5aai.fsf@email.froward.int.ebiederm.org> (raw)
In-Reply-To: <202308181317.66E6C9A5@keescook> (Kees Cook's message of "Fri, 18 Aug 2023 13:24:58 -0700")

Kees Cook <keescook@chromium.org> writes:

> On Fri, Aug 18, 2023 at 04:10:49PM -0400, Jeff Layton wrote:
>> [...]
>> extra checks (supposedly) compile down to nothing. It should be possible
>> to build alternate refcount_t handling functions that are just wrappers
>> around atomic_t with no extra checks, for folks who want to really run
>> "fast and loose".
>
> No -- there's no benefit for this. We already did all this work years
> ago with the fast vs full break-down. All that got tossed out since it
> didn't matter. We did all the performance benchmarking and there was no
> meaningful difference -- refcount _is_ atomic with an added check that
> is branch-predicted away. Peter Zijlstra and Will Deacon spent a lot of
> time making it run smoothly. :)

Since you did all of the work should the text size of be growing by a
kilobyte for this change?

Is that expected?

That is a valid concern with this change and it really should be
justified in the change long as someone brought it up.

Eric

  reply	other threads:[~2023-08-18 21:08 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-18  4:17 [PATCH v2] creds: Convert cred.usage to refcount_t Kees Cook
2023-08-18 17:55 ` Andrew Morton
2023-08-18 18:17   ` Jann Horn
2023-08-18 18:48     ` Kees Cook
2023-08-18 19:31       ` Andrew Morton
2023-08-18 20:10         ` Jeff Layton
2023-08-18 20:24           ` Kees Cook
2023-08-18 21:07             ` Eric W. Biederman [this message]
2023-08-21 10:18             ` David Laight
2023-08-18 20:16         ` Kees Cook
2023-08-18 20:54         ` Jann Horn
2023-08-18 18:46   ` Kees Cook
2023-08-18 20:21     ` David Windsor
2023-08-18 20:12 ` Jeff Layton

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