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Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg_or()'

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On Tue, Mar 15, 2016 at 2:32 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> I can see two other problems with it as well:
>
>  1) 'ptr' may get evaluated multiple times as well, not just 'mask'.

Right you are.

>  2) its naming sucks. "fetch_or()" does not really signal that it's a
>     fundamentally atomic operation, nor what API family it belongs to.

Actually, I like the naming, I just don't like the implementation.

It's not just the "evaluated multiple times", it's also the fact that
if we start doing "fetch_or()", then some day we'll want "fetch_and()"
or "fetch_clear()" etc.

Or, in fact, "fetch_add()", which is often closer to what hardware
does than the "atomic_add_return()" we have now (the difference is
that "fetch_add()" returns the original value, while
"atomic_add_return()" returns the end result).

So what I meant with "try to match what we already have in our
existing atomic.h" is that we do the _infrastructure_ so well. We do
it well both by having separate UP and SMP versions of the underlying
helpers, but we do it well by having those helpers that are then used
to implement the different atomic versions.

So I'd like something similar for the "fetch_op" thing.

                   Linus

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[GIT PULL] NOHZ updates for v4.6 Ingo Molnar <mingo@kernel.org> - 2016-03-14 13:40 +0100
  Re: [GIT PULL] NOHZ updates for v4.6 Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-15 03:50 +0100
    Re: [GIT PULL] NOHZ updates for v4.6 Peter Zijlstra <peterz@infradead.org> - 2016-03-15 09:50 +0100
      Re: [GIT PULL] NOHZ updates for v4.6 Ingo Molnar <mingo@kernel.org> - 2016-03-15 10:50 +0100
    [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg_or()' Ingo Molnar <mingo@kernel.org> - 2016-03-15 10:40 +0100
      Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Peter Zijlstra <peterz@infradead.org> - 2016-03-15 12:00 +0100
        Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Ingo Molnar <mingo@kernel.org> - 2016-03-15 13:10 +0100
          Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Peter Zijlstra <peterz@infradead.org> - 2016-03-15 13:50 +0100
      Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Peter Zijlstra <peterz@infradead.org> - 2016-03-15 12:10 +0100
      Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Ingo Molnar <mingo@kernel.org> - 2016-03-15 13:10 +0100
        Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Ingo Molnar <mingo@kernel.org> - 2016-03-15 13:40 +0100
          Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Ingo Molnar <mingo@kernel.org> - 2016-03-15 13:40 +0100
          Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Peter Zijlstra <peterz@infradead.org> - 2016-03-15 14:20 +0100
      Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Peter Zijlstra <peterz@infradead.org> - 2016-03-15 13:30 +0100
      [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Ingo Molnar <mingo@kernel.org> - 2016-03-15 13:30 +0100
        Re: [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Peter Zijlstra <peterz@infradead.org> - 2016-03-15 14:30 +0100
          Re: [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Ingo Molnar <mingo@kernel.org> - 2016-03-16 09:10 +0100
            Re: [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Peter Zijlstra <peterz@infradead.org> - 2016-03-16 09:40 +0100
        Re: [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Frederic Weisbecker <fweisbec@gmail.com> - 2016-03-15 18:10 +0100
          Re: [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Ingo Molnar <mingo@kernel.org> - 2016-03-16 09:20 +0100
            Re: [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to  'xchg_or()' Frederic Weisbecker <fweisbec@gmail.com> - 2016-03-17 02:00 +0100
      Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg_or()' Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-15 17:20 +0100
    [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to 'unsigned  int' Ingo Molnar <mingo@kernel.org> - 2016-03-15 11:00 +0100
      Re: [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to  'unsigned int' Ingo Molnar <mingo@kernel.org> - 2016-03-15 13:20 +0100
        Re: [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to  'unsigned int' Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-15 17:40 +0100
          Re: [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to  'unsigned int' Frederic Weisbecker <fweisbec@gmail.com> - 2016-03-15 18:30 +0100
            Re: [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to  'unsigned int' Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-15 18:40 +0100

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