Commit-ID: a4b575627e8d1a2498a921940813266d4e26ff56 Gitweb: http://git.kernel.org/tip/a4b575627e8d1a2498a921940813266d4e26ff56 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Wed, 7 Oct 2015 15:52:25 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Sat, 5 Dec 2015 12:33:26 -0800 documentation: Expand on scheduler/RCU deadlock requirements This commit adds a second option for avoiding scheduler/RCU deadlocks, namely that preemption be disabled across the entire RCU read-side critical section in question. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- Documentation/RCU/Design/Requirements/Requirements.html | 14 +++++++++----- Documentation/RCU/Design/Requirements/Requirements.htmlx | 14 +++++++++----- 2 files changed, 18 insertions(+), 10 deletions(-) diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index 1052471..ab513ed 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -1942,12 +1942,16 @@ RCU depends on the scheduler, and the scheduler uses RCU to protect some of its data structures. This means the scheduler is forbidden from acquiring the runqueue locks and the priority-inheritance locks -in the middle of an outermost RCU read-side critical section unless -it also releases them before exiting that same -RCU read-side critical section. -This same prohibition also applies to any lock that is acquired +in the middle of an outermost RCU read-side critical section unless either +(1) it releases them before exiting that same +RCU read-side critical section, or +(2) preemption is disabled across +that entire RCU read-side critical section. +This same prohibition also applies (recursively!) to any lock that is acquired while holding any lock to which this prohibition applies. -Violating this rule results in deadlock. +Adhering to this rule prevents preemptible RCU from invoking +<tt>rcu_read_unlock_special()</tt> while either runqueue or +priority-inheritance locks are held, thus avoiding deadlock. <p> For RCU's part, the preemptible-RCU <tt>rcu_read_unlock()</tt> diff --git a/Documentation/RCU/Design/Requirements/Requirements.htmlx b/Documentation/RCU/Design/Requirements/Requirements.htmlx index 5b76e21..f7c817f 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.htmlx +++ b/Documentation/RCU/Design/Requirements/Requirements.htmlx @@ -2109,12 +2109,16 @@ RCU depends on the scheduler, and the scheduler uses RCU to protect some of its data structures. This means the scheduler is forbidden from acquiring the runqueue locks and the priority-inheritance locks -in the middle of an outermost RCU read-side critical section unless -it also releases them before exiting that same -RCU read-side critical section. -This same prohibition also applies to any lock that is acquired +in the middle of an outermost RCU read-side critical section unless either +(1) it releases them before exiting that same +RCU read-side critical section, or +(2) preemption is disabled across +that entire RCU read-side critical section. +This same prohibition also applies (recursively!) to any lock that is acquired while holding any lock to which this prohibition applies. -Violating this rule results in deadlock. +Adhering to this rule prevents preemptible RCU from invoking +<tt>rcu_read_unlock_special()</tt> while either runqueue or +priority-inheritance locks are held, thus avoiding deadlock. <p> For RCU's part, the preemptible-RCU <tt>rcu_read_unlock()</tt> -- 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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