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Commit 84d82ec5 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
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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: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent b5016e82

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)