Commit-ID: 84d82ec5b9046ecdf16031d3e93a66ef50257402 Gitweb: http://git.kernel.org/tip/84d82ec5b9046ecdf16031d3e93a66ef50257402 Author: Thomas Gleixner <t...@linutronix.de> AuthorDate: Wed, 30 Nov 2016 21:04:45 +0000 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Fri, 2 Dec 2016 11:13:57 +0100
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 <t...@linutronix.de> Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: David Daney <dda...@caviumnetworks.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Mark Rutland <mark.rutl...@arm.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Sebastian Siewior <bige...@linutronix.de> Cc: Steven Rostedt <rost...@goodmis.org> Cc: Will Deacon <will.dea...@arm.com> Link: http://lkml.kernel.org/r/20161130210030.591941...@linutronix.de Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/locking/rtmutex.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 6e6cab7..2f443ed 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1619,11 +1619,15 @@ EXPORT_SYMBOL_GPL(__rt_mutex_init); * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a * proxy owner * - * @lock: the rt_mutex to be locked + * @lock: the rt_mutex to be locked * @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) @@ -1637,10 +1641,14 @@ void rt_mutex_init_proxy_locked(struct rt_mutex *lock, /** * rt_mutex_proxy_unlock - release a lock on behalf of owner * - * @lock: the rt_mutex to be locked + * @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)
