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locking/rtmutex: Explain locking rules for rt_mutex_proxy_unlock()/init_proxy_locked()
While debugging the unlock vs. dequeue race which resulted in state corruption of futexes the lockless nature of rt_mutex_proxy_unlock() caused some confusion. Add commentry to explain why it is safe to do this lockless. Add matching comments to rt_mutex_init_proxy_locked() for completeness sake. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sebastian Siewior <bigeasy@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/20161130210030.591941927@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -1619,11 +1619,15 @@ EXPORT_SYMBOL_GPL(__rt_mutex_init);
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* rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
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* proxy owner
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*
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* @lock: the rt_mutex to be locked
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* @lock: the rt_mutex to be locked
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* @proxy_owner:the task to set as owner
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*
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* No locking. Caller has to do serializing itself
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* Special API call for PI-futex support
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*
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* Special API call for PI-futex support. This initializes the rtmutex and
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* assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
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* possible at this point because the pi_state which contains the rtmutex
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* is not yet visible to other tasks.
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*/
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void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
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struct task_struct *proxy_owner)
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@ -1637,10 +1641,14 @@ void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
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/**
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* rt_mutex_proxy_unlock - release a lock on behalf of owner
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*
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* @lock: the rt_mutex to be locked
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* @lock: the rt_mutex to be locked
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*
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* No locking. Caller has to do serializing itself
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* Special API call for PI-futex support
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*
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* Special API call for PI-futex support. This merrily cleans up the rtmutex
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* (debugging) state. Concurrent operations on this rt_mutex are not
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* possible because it belongs to the pi_state which is about to be freed
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* and it is not longer visible to other tasks.
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*/
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void rt_mutex_proxy_unlock(struct rt_mutex *lock,
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struct task_struct *proxy_owner)
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