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

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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>
This commit is contained in:
Lai Jiangshan 2012-11-29 16:46:05 +08:00 • committed by Paul E. McKenney
parent ab4d2986e4
commit 3bc97a782c
1 changed files with 0 additions and 5 deletions
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5
include/linux/srcu.h
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@ -163,9 +163,6 @@ void srcu_barrier(struct srcu_struct *sp);
* power mode. This way we can notice an extended quiescent state to * power mode. This way we can notice an extended quiescent state to
* other CPUs that started a grace period. Otherwise we would delay any * other CPUs that started a grace period. Otherwise we would delay any
* grace period as long as we run in the idle task. * 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) 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; return 1;
if (rcu_is_cpu_idle()) if (rcu_is_cpu_idle())
return 0; return 0;
if (!rcu_lockdep_current_cpu_online())
return 0;
return lock_is_held(&sp->dep_map); return lock_is_held(&sp->dep_map);
} }