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Subject[PATCH v6 02/46] percpu_rwlock: Introduce per-CPU variables for the reader and the writer
Date
Per-CPU rwlocks ought to give better performance than global rwlocks.
That is where the "per-CPU" component comes in. So introduce the necessary
per-CPU variables that would be necessary at the reader and the writer sides,
and add the support for dynamically initializing per-CPU rwlocks.
These per-CPU variables will be used subsequently to implement the core
algorithm behind per-CPU rwlocks.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

include/linux/percpu-rwlock.h | 8 ++++++++
lib/percpu-rwlock.c | 12 ++++++++++++
2 files changed, 20 insertions(+)

diff --git a/include/linux/percpu-rwlock.h b/include/linux/percpu-rwlock.h
index 0caf81f..74eaf4d 100644
--- a/include/linux/percpu-rwlock.h
+++ b/include/linux/percpu-rwlock.h
@@ -28,7 +28,13 @@
#include <linux/lockdep.h>
#include <linux/spinlock.h>

+struct rw_state {
+ unsigned long reader_refcnt;
+ bool writer_signal;
+};
+
struct percpu_rwlock {
+ struct rw_state __percpu *rw_state;
rwlock_t global_rwlock;
};

@@ -41,6 +47,8 @@ extern void percpu_write_unlock(struct percpu_rwlock *);
extern int __percpu_init_rwlock(struct percpu_rwlock *,
const char *, struct lock_class_key *);

+extern void percpu_free_rwlock(struct percpu_rwlock *);
+
#define percpu_init_rwlock(pcpu_rwlock) \
({ static struct lock_class_key rwlock_key; \
__percpu_init_rwlock(pcpu_rwlock, #pcpu_rwlock, &rwlock_key); \
diff --git a/lib/percpu-rwlock.c b/lib/percpu-rwlock.c
index 111a238..f938096 100644
--- a/lib/percpu-rwlock.c
+++ b/lib/percpu-rwlock.c
@@ -31,6 +31,10 @@
int __percpu_init_rwlock(struct percpu_rwlock *pcpu_rwlock,
const char *name, struct lock_class_key *rwlock_key)
{
+ pcpu_rwlock->rw_state = alloc_percpu(struct rw_state);
+ if (unlikely(!pcpu_rwlock->rw_state))
+ return -ENOMEM;
+
/* ->global_rwlock represents the whole percpu_rwlock for lockdep */
#ifdef CONFIG_DEBUG_SPINLOCK
__rwlock_init(&pcpu_rwlock->global_rwlock, name, rwlock_key);
@@ -41,6 +45,14 @@ int __percpu_init_rwlock(struct percpu_rwlock *pcpu_rwlock,
return 0;
}

+void percpu_free_rwlock(struct percpu_rwlock *pcpu_rwlock)
+{
+ free_percpu(pcpu_rwlock->rw_state);
+
+ /* Catch use-after-free bugs */
+ pcpu_rwlock->rw_state = NULL;
+}
+
void percpu_read_lock(struct percpu_rwlock *pcpu_rwlock)
{
read_lock(&pcpu_rwlock->global_rwlock);


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