locking/rtmutex: Explain locking rules for rt_mutex_proxy_unlock()/init_proxy_locked() (84d82ec5) · Commits · 戴 / test

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>

kernel/locking/rtmutex.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -1623,7 +1623,11 @@ EXPORT_SYMBOL_GPL(__rt_mutex_init);
		* @proxy_owner:the task to set as owner
		*
		* No locking. Caller has to do serializing itself
		* Special API call for PI-futex support
		*
		* Special API call for PI-futex support. This initializes the rtmutex and
		* assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
		* possible at this point because the pi_state which contains the rtmutex
		* is not yet visible to other tasks.
		*/
		void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
		struct task_struct *proxy_owner)
		@@ -1640,7 +1644,11 @@ void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
		* @lock: the rt_mutex to be locked
		*
		* No locking. Caller has to do serializing itself
		* Special API call for PI-futex support
		*
		* Special API call for PI-futex support. This merrily cleans up the rtmutex
		* (debugging) state. Concurrent operations on this rt_mutex are not
		* possible because it belongs to the pi_state which is about to be freed
		* and it is not longer visible to other tasks.
		*/
		void rt_mutex_proxy_unlock(struct rt_mutex *lock,
		struct task_struct *proxy_owner)

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