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authorOleg Nesterov <oleg@redhat.com>2014-09-29 01:44:21 +0400
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-11-13 21:35:40 +0300
commitce36f2f3eb6613a73bc6f3a5256bde7dd3f95710 (patch)
tree7c225c914aabb54c7ce3add5917386f27e67990a /include/linux/rcupdate.h
parentb6331ae8afe4118884c4b6e14a213758d88422b2 (diff)
downloadlinux-ce36f2f3eb6613a73bc6f3a5256bde7dd3f95710.tar.xz
rcu: More info about potential deadlocks with rcu_read_unlock()
The comment above rcu_read_unlock() explains the potential deadlock if the caller holds one of the locks taken by rt_mutex_unlock() paths, but it is not clear from this documentation that any lock which can be taken from interrupt can lead to deadlock as well and we need to take rt_mutex_lock() into account too. The problem is that rt_mutex_lock() takes wait_lock without disabling irqs, and thus an interrupt taking some LOCK can obviously race with rcu_read_unlock_special() called with the same LOCK held. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'include/linux/rcupdate.h')
-rw-r--r--include/linux/rcupdate.h4
1 files changed, 3 insertions, 1 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 36ea3ba5c516..ae6942a84a0d 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -887,7 +887,9 @@ static inline void rcu_read_lock(void)
* Unfortunately, this function acquires the scheduler's runqueue and
* priority-inheritance spinlocks. This means that deadlock could result
* if the caller of rcu_read_unlock() already holds one of these locks or
- * any lock that is ever acquired while holding them.
+ * any lock that is ever acquired while holding them; or any lock which
+ * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
+ * does not disable irqs while taking ->wait_lock.
*
* That said, RCU readers are never priority boosted unless they were
* preempted. Therefore, one way to avoid deadlock is to make sure