Commit-ID: ce36f2f3eb6613a73bc6f3a5256bde7dd3f95710 Gitweb: http://git.kernel.org/tip/ce36f2f3eb6613a73bc6f3a5256bde7dd3f95710 Author: Oleg Nesterov <oleg@xxxxxxxxxx> AuthorDate: Sun, 28 Sep 2014 23:44:21 +0200 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Thu, 13 Nov 2014 10:35:40 -0800 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@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- include/linux/rcupdate.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 36ea3ba..ae6942a 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 -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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