Commit 3bc97a78 authored Nov 29, 2012 by Lai Jiangshan Committed by Paul E. McKenney Feb 07, 2013

srcu: Remove checks preventing offline CPUs from calling srcu_read_lock()



SRCU has its own statemachine and no longer relies on normal RCU.
Its read-side critical section can now be used by an offline CPU, so this
commit removes the check and the comments, reverting the SRCU portion
of c0d6d01b (rcu: Check for illegal use of RCU from offlined CPUs).

It also makes the code match the comments in whatisRCU.txt:

g.	Do you need read-side critical sections that are respected
	even though they are in the middle of the idle loop, during
	user-mode execution, or on an offlined CPU?  If so, SRCU is the
	only choice that will work for you.

[ paulmck: There is at least one remaining issue, namely use of lockdep
	   with tracing enabled. ]

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent ab4d2986

include/linux/srcu.h

+0 −5

Original line number	Diff line number	Diff line
		@@ -163,9 +163,6 @@ void srcu_barrier(struct srcu_struct *sp);
		* power mode. This way we can notice an extended quiescent state to
		* other CPUs that started a grace period. Otherwise we would delay any
		* grace period as long as we run in the idle task.
		*
		* Similarly, we avoid claiming an SRCU read lock held if the current
		* CPU is offline.
		*/
		static inline int srcu_read_lock_held(struct srcu_struct *sp)
		{
		@@ -173,8 +170,6 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
		return 1;
		if (rcu_is_cpu_idle())
		return 0;
		if (!rcu_lockdep_current_cpu_online())
		return 0;
		return lock_is_held(&sp->dep_map);
		}