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Subject[PATCH -v2 6/7] locking/percpu-rwsem: Fold __percpu_up_read()
From: Davidlohr Bueso <dave@stgolabs.net>

Now that __percpu_up_read() is only ever used from percpu_up_read()
merge them, it's a small function.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/percpu-rwsem.h | 19 +++++++++++++++----
kernel/exit.c | 1 +
kernel/locking/percpu-rwsem.c | 15 ---------------
3 files changed, 16 insertions(+), 19 deletions(-)

--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -43,7 +43,6 @@ is_static struct percpu_rw_semaphore nam
__DEFINE_PERCPU_RWSEM(name, static)

extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool);
-extern void __percpu_up_read(struct percpu_rw_semaphore *);

static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
{
@@ -103,10 +102,22 @@ static inline void percpu_up_read(struct
/*
* Same as in percpu_down_read().
*/
- if (likely(rcu_sync_is_idle(&sem->rss)))
+ if (likely(rcu_sync_is_idle(&sem->rss))) {
__this_cpu_dec(*sem->read_count);
- else
- __percpu_up_read(sem); /* Unconditional memory barrier */
+ } else {
+ /*
+ * slowpath; reader will only ever wake a single blocked
+ * writer.
+ */
+ smp_mb(); /* B matches C */
+ /*
+ * In other words, if they see our decrement (presumably to
+ * aggregate zero, as that is the only time it matters) they
+ * will also see our critical section.
+ */
+ __this_cpu_dec(*sem->read_count);
+ rcuwait_wake_up(&sem->writer);
+ }
preempt_enable();
}

--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -258,6 +258,7 @@ void rcuwait_wake_up(struct rcuwait *w)
wake_up_process(task);
rcu_read_unlock();
}
+EXPORT_SYMBOL_GPL(rcuwait_wake_up);

/*
* Determine if a process group is "orphaned", according to the POSIX
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -177,21 +177,6 @@ bool __percpu_down_read(struct percpu_rw
}
EXPORT_SYMBOL_GPL(__percpu_down_read);

-void __percpu_up_read(struct percpu_rw_semaphore *sem)
-{
- smp_mb(); /* B matches C */
- /*
- * In other words, if they see our decrement (presumably to aggregate
- * zero, as that is the only time it matters) they will also see our
- * critical section.
- */
- __this_cpu_dec(*sem->read_count);
-
- /* Prod writer to re-evaluate readers_active_check() */
- rcuwait_wake_up(&sem->writer);
-}
-EXPORT_SYMBOL_GPL(__percpu_up_read);
-
#define per_cpu_sum(var) \
({ \
typeof(var) __sum = 0; \

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