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Message-ID: <CAGXu5jJY2cD=nTVdv9PsAgBaJ-9KMnR5NWFScWmc_KQSSWY01Q@mail.gmail.com>
Date: Mon, 24 Apr 2017 13:19:24 -0700
From: Kees Cook <keescook@...omium.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Eric Biggers <ebiggers3@...il.com>,
Christoph Hellwig <hch@...radead.org>, "axboe@...nel.dk" <axboe@...nel.dk>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Elena Reshetova <elena.reshetova@...el.com>, Hans Liljestrand <ishkamiel@...il.com>,
David Windsor <dwindsor@...il.com>, "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jann Horn <jann@...jh.net>,
"David S. Miller" <davem@...emloft.net>, linux-arch <linux-arch@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, PaX Team <pageexec@...email.hu>
Subject: Re: [PATCH] x86/refcount: Implement fast refcount_t handling
On Mon, Apr 24, 2017 at 3:45 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Apr 21, 2017 at 03:09:39PM -0700, Kees Cook wrote:
>> +static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r)
>> +{
>> + const int a = 1;
>> + const int u = 0;
>> + int c, old;
>> +
>> + c = atomic_read(&(r->refs));
>> + for (;;) {
>> + if (unlikely(c == (u)))
>> + break;
>> + old = atomic_cmpxchg(&(r->refs), c, c + (a));
>
> Please use atomic_try_cmpxchg(), that generates saner code.
Ah-ha, thanks. I actually copied this directly out of the existing
atomic_t function, so we should probably update it there too.
-Kees
>
>> + if (likely(old == c))
>> + break;
>> + c = old;
>> + }
>> + return c != u;
>> +}
--
Kees Cook
Pixel Security
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