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documentation: Expand on scheduler/RCU deadlock requirements

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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>
This commit is contained in:
Paul E. McKenney 2015-10-07 15:52:25 -07:00
parent 0825458b1d
commit a4b575627e
2 changed files with 18 additions and 10 deletions
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14
Documentation/RCU/Design/Requirements/Requirements.html
View file

@ -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>

14
Documentation/RCU/Design/Requirements/Requirements.htmlx
View file

@ -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>