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Re: [RFC][PATCH 7/7] kref: Implement using refcount_t

From Boqun Feng <boqun.feng@gmail.com>
Newsgroups linux.kernel
Subject Re: [RFC][PATCH 7/7] kref: Implement using refcount_t
Date 2016-11-21 09:40 +0100
Message-ID <sFSiS-7gi-15@gated-at.bofh.it> (permalink)
References (2 earlier) <sEOhk-5Ju-25@gated-at.bofh.it> <sEPGq-6vc-33@gated-at.bofh.it> <sEUPM-1xM-33@gated-at.bofh.it> <sFO5z-4xa-3@gated-at.bofh.it> <sFRwu-6Fr-7@gated-at.bofh.it>
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On Mon, Nov 21, 2016 at 08:48:26AM +0100, Ingo Molnar wrote:
> 
> * Boqun Feng <boqun.feng@gmail.com> wrote:
> 
> > > It also fails to decrement in the underflow case (which is fine, but not
> > > obvious from the comment). Same thing below.
> > > 
> > 
> > Maybe a table in the comment like the following helps?
> > 
> > /*
> >  * T: return true, F: return fasle
> >  * W: trigger WARNING
> >  * N: no effect
> >  *
> >  *                      |       value before ops                  |
> >  *                      |   0   |   1   | UINT_MAX - 1 | UINT_MAX |
> >  * ---------------------+-------+-------+--------------+----------+
> >  * inc()                |  W    |       |      W       |      N   |
> >  * inc_not_zero()       |   FN  |   T   |      WT      |    WTN   |
> >  * dec_and_test()       |  WFN  |   T   |       F      |     FN   |
> >  * dec_and_mutex_lock() |  WFN  |   T   |       F      |     FN   |
> >  * dec_and_spin_lock()  |  WFN  |   T   |       F      |     FN   |
> >  */
> 
> Yes!
> 
> nit: s/fasle/false
> 
> Also, I think we want to do a couple of other changes as well to make it more 
> readable, extend the columns with 'normal' values (2 and UINT_MAX-2) and order the 
> colums properly. I.e. something like:
> 
> /*
>  * The before/after outcome of various atomic ops:
>  *
>  *   T: returns true
>  *   F: returns false
>  *   ----------------------------------
>  *   W: op triggers kernel WARNING
>  *   ----------------------------------
>  *   0: no change to atomic var value
>  *   +: atomic var value increases by 1
>  *   -: atomic var value decreases by 1
>  *   ----------------------------------
>  *  -1: UINT_MAX
>  *  -2: UINT_MAX-1
>  *  -3: UINT_MAX-2
>  *
>  * ---------------------+-----+-----+-----+-----+-----+-----+
>  * value before:        |  -3 |  -2 |  -1 |   0 |   1 |   2 |
>  * ---------------------+-----+-----+-----+-----+-----+-----+
>  * value+effect after:                                      |
>  * ---------------------+     |     |     |     |     |     |
>  * inc()                | ..+ | W.+ | ..0 | W.+ | ..+ | ..+ |
>  * inc_not_zero()       | .T+ | WT+ | WT0 | .F0 | .T+ | .T+ |
>  * dec_and_test()       | .F- | .F- | .F0 | WF0 | .T- | .F- |
>  * dec_and_mutex_lock() | .F- | .F- | .F0 | WF0 | .T- | .F- |
>  * dec_and_spin_lock()  | .F- | .F- | .F0 | WF0 | .T- | .F- |
>  * ---------------------+-----+-----+-----+-----+-----+-----+
>  *
>  * So for example: 'WT+' in the inc_not_zero() row and '-2' column
>  * means that when the atomic_inc_not_zero() function is called
>  * with an atomic var that has a value of UINT_MAX-1, then the
>  * atomic var's value will increase to the maximum overflow value
>  * of UINT_MAX and will produce a warning. The function returns
>  * 'true'.
>  */
> 
> I think this table makes the overflow/underflow semantics pretty clear and also 
> documents the regular behavior of these atomic ops pretty intuitively.
> 
> Agreed?
> 

Sure, this looks pretty great! Much more informative and readable than
my version ;-) Thank you.

Regards,
Boqun

> Thanks,
> 
> 	Ingo

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[RFC][PATCH 0/7] kref improvements Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
  [RFC][PATCH 5/7] kref: Implement kref_put_lock() Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
    Re: [RFC][PATCH 5/7] kref: Implement kref_put_lock() Kees Cook <keescook@chromium.org> - 2016-11-14 21:40 +0100
      Re: [RFC][PATCH 5/7] kref: Implement kref_put_lock() Peter Zijlstra <peterz@infradead.org> - 2016-11-15 09:00 +0100
  [RFC][PATCH 6/7] kref: Avoid more abuse Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
  [RFC][PATCH 4/7] kref: Use kref_get_unless_zero() more Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
  [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
    Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-15 09:50 +0100
      Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-15 10:50 +0100
        Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-15 11:10 +0100
          Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-15 11:50 +0100
            Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-15 14:10 +0100
              Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-15 19:10 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-15 20:20 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-15 20:30 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-16 09:40 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 10:00 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-16 10:10 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 10:30 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-16 11:20 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-16 20:00 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 09:40 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-17 21:00 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-16 19:50 +0100
    Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-15 13:40 +0100
      Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-15 14:10 +0100
        Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-15 15:20 +0100
          Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 10:30 +0100
            Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-17 10:50 +0100
              Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 11:40 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 11:50 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Greg KH <gregkh@linuxfoundation.org> - 2016-11-17 12:10 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:10 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:30 +0100
            Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Will Deacon <will.deacon@arm.com> - 2016-11-17 18:10 +0100
              Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-18 09:30 +0100
                Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Will Deacon <will.deacon@arm.com> - 2016-11-18 11:20 +0100
            Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Will Deacon <will.deacon@arm.com> - 2016-11-17 18:10 +0100
              Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:30 +0100
    RE: [RFC][PATCH 7/7] kref: Implement using refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-18 11:10 +0100
      Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-18 12:40 +0100
        Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Will Deacon <will.deacon@arm.com> - 2016-11-18 18:10 +0100
          Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-18 20:00 +0100
          Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-21 05:10 +0100
            Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-21 08:50 +0100
              Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-21 09:40 +0100
        Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-21 09:50 +0100
          Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-21 10:10 +0100
            Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-21 10:40 +0100
    RE: [RFC][PATCH 7/7] kref: Implement using refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-18 11:50 +0100
      Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-18 12:00 +0100
        RE: [RFC][PATCH 7/7] kref: Implement using refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-18 18:00 +0100
          Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-18 20:00 +0100
            RE: [RFC][PATCH 7/7] kref: Implement using refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-19 08:20 +0100
              Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-19 12:50 +0100
  Re: [RFC][PATCH 2/7] kref: Add kref_read() Christoph Hellwig <hch@infradead.org> - 2016-11-14 19:20 +0100
    Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-15 08:30 +0100
      Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-15 08:50 +0100
      [PATCH] printk, locking/atomics, kref: Introduce new %pAr and %pAk  format string options for atomic_t and 'struct kref' Ingo Molnar <mingo@kernel.org> - 2016-11-15 09:40 +0100
        [PATCH v2] printk, locking/atomics, kref: Introduce new %pAr and  %pAk format string options for atomic_t and 'struct kref' Ingo Molnar <mingo@kernel.org> - 2016-11-15 09:50 +0100
          Re: [PATCH v2] printk, locking/atomics, kref: Introduce new %pAr and  %pAk format string options for atomic_t and 'struct kref' Peter Zijlstra <peterz@infradead.org> - 2016-11-15 10:30 +0100
            [PATCH v3] printk, locking/atomics, kref: Introduce new %pAa and  %pAk format string options for atomic_t and 'struct kref' Ingo Molnar <mingo@kernel.org> - 2016-11-15 10:50 +0100
          Re: [PATCH v2] printk, locking/atomics, kref: Introduce new %pAr and  %pAk format string options for atomic_t and 'struct kref' kbuild test robot <lkp@intel.com> - 2016-11-15 11:10 +0100
        Re: [PATCH] printk, locking/atomics, kref: Introduce new %pAr and  %pAk format string options for atomic_t and 'struct kref' Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-15 17:50 +0100
          Re: [PATCH] printk, locking/atomics, kref: Introduce new %pAr and  %pAk format string options for atomic_t and 'struct kref' Ingo Molnar <mingo@kernel.org> - 2016-11-16 09:20 +0100
  Re: [RFC][PATCH 0/7] kref improvements Greg KH <gregkh@linuxfoundation.org> - 2016-11-15 08:30 +0100
    Re: [RFC][PATCH 0/7] kref improvements Ingo Molnar <mingo@kernel.org> - 2016-11-15 08:50 +0100
      Re: [RFC][PATCH 0/7] kref improvements Greg KH <gregkh@linuxfoundation.org> - 2016-11-15 16:10 +0100
    Re: [RFC][PATCH 0/7] kref improvements Peter Zijlstra <peterz@infradead.org> - 2016-11-15 08:50 +0100
  Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-15 08:40 +0100
    Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-15 09:10 +0100
      Re: [RFC][PATCH 2/7] kref: Add kref_read() Kees Cook <keescook@chromium.org> - 2016-11-15 22:00 +0100
        Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 09:30 +0100
          Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-16 11:20 +0100
            Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 11:20 +0100
          Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 11:20 +0100
          Re: [RFC][PATCH 2/7] kref: Add kref_read() Daniel Borkmann <daniel@iogearbox.net> - 2016-11-16 11:20 +0100
        Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-16 11:10 +0100
          Re: [RFC][PATCH 2/7] kref: Add kref_read() Kees Cook <keescook@chromium.org> - 2016-11-16 20:00 +0100
            Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 09:40 +0100
              Re: [RFC][PATCH 2/7] kref: Add kref_read() David Windsor <dave@progbits.org> - 2016-11-17 13:50 +0100
                RE: [RFC][PATCH 2/7] kref: Add kref_read() "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-17 15:40 +0100
                Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:10 +0100
                RE: [RFC][PATCH 2/7] kref: Add kref_read() "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-17 18:10 +0100
                RE: [RFC][PATCH 2/7] kref: Add kref_read() "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-17 19:10 +0100
                Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 20:20 +0100
                Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 20:40 +0100
                Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:20 +0100
              Re: [RFC][PATCH 2/7] kref: Add kref_read() Kees Cook <keescook@chromium.org> - 2016-11-17 20:40 +0100

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