[PATCH] rcu: Remove superfluous versions of rcu_read_lock_sched_held()
From: Boqun Feng
Date: Wed Mar 23 2016 - 11:12:43 EST
Currently, we have four versions of rcu_read_lock_sched_held(),
depending on the combined choices on PREEMPT_COUNT and DEBUG_LOCK_ALLOC.
But we actually don't need to specialize those for PREEMPT_COUNT=n
kernel. Because:
1. For the implementations in DEBUG_LOCK_ALLOC=n kernel, we can use
preemptible() to implement one rcu_read_lock_sched_held(), which
gives us the same behavior as the current two.
2. For the implementations in DEBUG_LOCK_ALLOC=y kernel, even when
PREEMPT_COUNT=n, one CPU may block no grace period because of
the same reason for the PREEMPT_COUNT=y and !PREEMPT kernel.
(e.g. dynticks or cpu hotplug)
So unify the implementations of rcu_read_lock_sched_held() by using
macro preemptible() and tightening up the lock-held checking for
PREEMPT_COUNT=n kernel. And this will improve the readability, make the
debug checking as expected and save several lines of code.
Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
---
include/linux/rcupdate.h | 17 +----------------
kernel/rcu/update.c | 4 ++--
2 files changed, 3 insertions(+), 18 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b5d48bd..e3f845b 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -510,14 +510,7 @@ int rcu_read_lock_bh_held(void);
* CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
* critical section unless it can prove otherwise.
*/
-#ifdef CONFIG_PREEMPT_COUNT
int rcu_read_lock_sched_held(void);
-#else /* #ifdef CONFIG_PREEMPT_COUNT */
-static inline int rcu_read_lock_sched_held(void)
-{
- return 1;
-}
-#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -534,18 +527,10 @@ static inline int rcu_read_lock_bh_held(void)
return 1;
}
-#ifdef CONFIG_PREEMPT_COUNT
static inline int rcu_read_lock_sched_held(void)
{
- return preempt_count() != 0 || irqs_disabled();
+ return !preemptible();
}
-#else /* #ifdef CONFIG_PREEMPT_COUNT */
-static inline int rcu_read_lock_sched_held(void)
-{
- return 1;
-}
-#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
-
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
#ifdef CONFIG_PROVE_RCU
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index ca828b4..3ccdc8e 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -67,7 +67,7 @@ static int rcu_normal_after_boot;
module_param(rcu_normal_after_boot, int, 0);
#endif /* #ifndef CONFIG_TINY_RCU */
-#if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT)
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
/**
* rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
*
@@ -111,7 +111,7 @@ int rcu_read_lock_sched_held(void)
return 0;
if (debug_locks)
lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
- return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
+ return lockdep_opinion || !preemptible();
}
EXPORT_SYMBOL(rcu_read_lock_sched_held);
#endif
--
2.7.3