Commit a4b57562 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 0825458b

Documentation/RCU/Design/Requirements/Requirements.html

+9 −5
Original line number Diff line number Diff line
@@ -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>

Documentation/RCU/Design/Requirements/Requirements.htmlx

+9 −5
Original line number Diff line number Diff line
@@ -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>

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