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authorThomas Gleixner <tglx@linutronix.de>2016-11-30 21:04:45 +0000
committerIngo Molnar <mingo@kernel.org>2016-12-02 11:13:57 +0100
commit84d82ec5b9046ecdf16031d3e93a66ef50257402 (patch)
tree716c8ca677edf6cc92677f7a647cdd9bfa641af9 /kernel/locking
parentb5016e8203003c44264ec88fe2276ff54a51f689 (diff)
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>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rtmutex.c16
1 files changed, 12 insertions, 4 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 6e6cab7ac12f..2f443ed2320a 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)