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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-10-07 15:52:25 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-12-05 12:33:26 -0800
commita4b575627e8d1a2498a921940813266d4e26ff56 (patch)
tree297bf78c5c5c4ca2bc7530ef6f2a5a2fca7359dd /Documentation/RCU
parent0825458b1dbc39ec6840ee2e45b1fedb1b4b4ca1 (diff)
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@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/Design/Requirements/Requirements.html14
-rw-r--r--Documentation/RCU/Design/Requirements/Requirements.htmlx14
2 files changed, 18 insertions, 10 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index 105247149975..ab513ed229d7 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)&nbsp;it releases them before exiting that same
+RCU read-side critical section, or
+(2)&nbsp;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 5b76e21fa092..f7c817f235e0 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)&nbsp;it releases them before exiting that same
+RCU read-side critical section, or
+(2)&nbsp;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>