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Re: [PATCH -v6 04/13] futex,rt_mutex: Provide futex specific rt_mutex API

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On Wed, Mar 22, 2017 at 11:35:51AM +0100, Peter Zijlstra wrote:
> Part of what makes futex_unlock_pi() intricate is that
> rt_mutex_futex_unlock() -> rt_mutex_slowunlock() can drop
> rt_mutex::wait_lock.
> 
> This means we cannot rely on the atomicy of wait_lock, which we would
> like to do in order to not rely on hb->lock so much.
> 
> The reason rt_mutex_slowunlock() needs to drop wait_lock is because it
> can race with the rt_mutex fastpath, however futexes have their own
> fast path.
> 
> Since futexes already have a bunch of separate rt_mutex accessors,
> complete that set and implement a rt_mutex variant without fastpath
> for them.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Got to here and tried to get some testing going while I was reviewing... to find
that some of the existing pi test suites LTP/realtime, are not building either.
Got a fix, got it into CI, some CI issues, but no obvious fallout from this. So,
review will continue...

But, Peter are you testing this with anything in particular?

-- 
Darren Hart
VMware Open Source Technology Center

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[PATCH -v6 00/13] The arduous story of FUTEX_UNLOCK_PI Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
  [PATCH -v6 10/13] futex,rt_mutex: Restructure rt_mutex_finish_proxy_lock() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex,rt_mutex: Restructure  rt_mutex_finish_proxy_lock() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 07/13] futex: Rework inconsistent rt_mutex/futex_q state Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Rework inconsistent rt_mutex/futex_q  state tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 09/13] futex,rt_mutex: Introduce rt_mutex_init_waiter() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex,rt_mutex: Introduce rt_mutex_init_waiter() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 05/13] futex: Change locking rules Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Change locking rules tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 11/13] futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Rework futex_lock_pi() to use  rt_mutex_*_proxy_lock() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 13/13] futex: futex_lock_pi() vs PREEMPT_RT_FULL Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Drop hb->lock before enqueueing on the  rtmutex tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 03/13] futex: Remove rt_mutex_deadlock_account_*() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Remove rt_mutex_deadlock_account_*() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
    Re: [PATCH -v6 03/13] futex: Remove rt_mutex_deadlock_account_*() Darren Hart <dvhart@infradead.org> - 2017-03-24 22:30 +0100
      Re: [PATCH -v6 03/13] futex: Remove rt_mutex_deadlock_account_*() Darren Hart <dvhart@infradead.org> - 2017-03-24 22:40 +0100
  [PATCH -v6 12/13] futex: futex_unlock_pi() determinism Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Futex_unlock_pi() determinism tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 06/13] futex: Cleanup refcounting Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Cleanup refcounting tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 04/13] futex,rt_mutex: Provide futex specific rt_mutex API Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex,rt_mutex: Provide futex specific rt_mutex  API tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
    Re: [PATCH -v6 04/13] futex,rt_mutex: Provide futex specific  rt_mutex API Darren Hart <dvhart@infradead.org> - 2017-03-25 01:40 +0100
  [PATCH -v6 02/13] futex: Use smp_store_release() in mark_wake_futex() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Use smp_store_release() in  mark_wake_futex() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
    Re: [PATCH -v6 02/13] futex: Use smp_store_release() in  mark_wake_futex() Darren Hart <dvhart@infradead.org> - 2017-03-24 22:20 +0100
  Re: [PATCH -v6 00/13] The arduous story of FUTEX_UNLOCK_PI Darren Hart <dvhart@infradead.org> - 2017-03-24 02:50 +0100

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