Resolving RCU-scheduler deadlocks

In a computer system having one or more processors operatively coupled to one or more memory devices and implementing a read-copy update (RCU) subsystem, a method for resolving deadlocks between said RCU subsystem and an operating system scheduler, comprising:

• providing an RCU registration component that allows an RCU reader to manipulate an rcu_read_lock_nesting counter when said RCU reader enters an RCU read-side critical section;
• providing an RCU unregistration component that allows an RCU reader to manipulate said rcu_read_lock_nesting counter when said RCU reader leaves an RCU read-side critical section;
• said unregistration component providing first and second rcu_read_lock_nesting manipulation paths that are dependent on a current value of said rcu_read_lock_nesting counter;
• said first rcu_read_lock_nesting manipulation path being taken when said current value of said rcu_read_lock_nesting counter is indicative of a task-context RCU reader exiting an outermost RCU read-side critical section;
• said first rcu_read_lock_nesting manipulation path including condition-based read-side helper processing that may result in invocation of said operating system scheduler;
• said first rcu_read_lock_nesting manipulation path further including a deadlock protection operation that temporarily manipulates said rcu_read_lock_nesting counter to prevent any intervening RCU reader from taking said first rcu_read_lock_nesting manipulation path while a task-context RCU reader is within that path;
• said second rcu_read_lock_nesting manipulation path being taken when said current value of said rcu_read_lock_nesting counter is indicative of a task-context RCU reader exiting a non-outermost RCU read-side critical section or an RCU reader being nested within said first rcu_read_lock_nesting manipulation path;
• said second rcu_read_lock_nesting manipulation path bypassing said condition-based read-side helper processing
• said RCU unregistration component allowing an RCU reader to manipulate said rcu_read_lock_nesting counter by either decrementing it or setting it to a value, depending on which manipulation path is taken by said RCU reader;
• and
• said first manipulation path comprising setting said rcu_read_lock_nesting counter to a deadlock protection value and said second manipulation path comprises decrementing said rcu_read_lock_nesting counter.