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authorLai Jiangshan <laijs@cn.fujitsu.com>2012-11-29 16:46:06 +0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2013-02-07 15:15:00 -0800
commit511a0868bed6694512348fc177cdfaf3fd97d0bb (patch)
tree2875f25752a987492ce88169177dfae857542d9d /include/linux/srcu.h
parent3bc97a782cc8c112f64a25143452b06206364cc8 (diff)
srcu: Remove checks preventing idle 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 ff195cb6 (rcu: Warn when srcu_read_lock() is used in an extended quiescent state). It also makes the codes 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>
Diffstat (limited to 'include/linux/srcu.h')
-rw-r--r--include/linux/srcu.h21
1 files changed, 3 insertions, 18 deletions
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index ae3ee39eb699..04f4121a23ae 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -151,25 +151,14 @@ void srcu_barrier(struct srcu_struct *sp);
* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
* and while lockdep is disabled.
*
- * Note that if the CPU is in the idle loop from an RCU point of view
- * (ie: that we are in the section between rcu_idle_enter() and
- * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
- * the CPU did an srcu_read_lock(). The reason for this is that RCU
- * ignores CPUs that are in such a section, considering these as in
- * extended quiescent state, so such a CPU is effectively never in an
- * RCU read-side critical section regardless of what RCU primitives it
- * invokes. This state of affairs is required --- we need to keep an
- * RCU-free window in idle where the CPU may possibly enter into low
- * 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.
+ * Note that SRCU is based on its own statemachine and it doesn't
+ * relies on normal RCU, it can be called from the CPU which
+ * is in the idle loop from an RCU point of view or offline.
*/
static inline int srcu_read_lock_held(struct srcu_struct *sp)
{
if (!debug_lockdep_rcu_enabled())
return 1;
- if (rcu_is_cpu_idle())
- return 0;
return lock_is_held(&sp->dep_map);
}
@@ -231,8 +220,6 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
int retval = __srcu_read_lock(sp);
rcu_lock_acquire(&(sp)->dep_map);
- rcu_lockdep_assert(!rcu_is_cpu_idle(),
- "srcu_read_lock() used illegally while idle");
return retval;
}
@@ -246,8 +233,6 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
__releases(sp)
{
- rcu_lockdep_assert(!rcu_is_cpu_idle(),
- "srcu_read_unlock() used illegally while idle");
rcu_lock_release(&(sp)->dep_map);
__srcu_read_unlock(sp, idx);
}