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Re: [PATCH] x86/refcount: Implement fast refcount_t handling

From Kees Cook <keescook@chromium.org>
Newsgroups linux.kernel
Subject Re: [PATCH] x86/refcount: Implement fast refcount_t handling
Date 2017-04-24 22:20 +0200
Message-ID <tzSCK-37e-7@gated-at.bofh.it> (permalink)
References <tyOUy-2RV-13@gated-at.bofh.it> <tzJJ8-5V5-21@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Mon, Apr 24, 2017 at 3:45 AM, Peter Zijlstra <peterz@infradead.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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Thread

[PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-22 00:10 +0200
  Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 10:40 +0200
    Re: [kernel-hardening] Re: [PATCH] x86/refcount: Implement fast  refcount_t handling Jann Horn <jannh@google.com> - 2017-04-24 11:00 +0200
      Re: [kernel-hardening] Re: [PATCH] x86/refcount: Implement fast  refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 11:30 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-24 13:10 +0200
      Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 13:20 +0200
        Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-24 15:20 +0200
          Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 15:40 +0200
            Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-24 17:20 +0200
              Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:50 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-25 00:10 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-25 00:40 +0200
                Re: [kernel-hardening] Re: [PATCH] x86/refcount: Implement fast  refcount_t handling Rik van Riel <riel@redhat.com> - 2017-04-25 03:20 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-25 11:10 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-25 13:30 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-25 18:40 +0200
      Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:40 +0200
        Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-25 13:30 +0200
          Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-25 18:50 +0200
            Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-26 04:20 +0200
              Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-26 06:50 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:20 +0200
  Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 12:50 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:20 +0200
  Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 13:00 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:30 +0200
  Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-25 12:30 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-25 13:30 +0200

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