[PATCH v5 02/45] percpu_rwlock: Introduce per-CPU variables for the reader and the writer
From: Srivatsa S. Bhat <hidden>
Date: 2013-01-22 07:35:32
Also in:
linux-arch, linux-arm-kernel, linuxppc-dev, lkml, netdev
Subsystem:
library code, per-cpu memory allocator, the rest · Maintainers:
Andrew Morton, Dennis Zhou, Tejun Heo, Christoph Lameter, Linus Torvalds
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 <redacted> --- include/linux/percpu-rwlock.h | 4 ++++ lib/percpu-rwlock.c | 21 +++++++++++++++++++++ 2 files changed, 25 insertions(+)
diff --git a/include/linux/percpu-rwlock.h b/include/linux/percpu-rwlock.h
index 45620d0..cd5eab5 100644
--- a/include/linux/percpu-rwlock.h
+++ b/include/linux/percpu-rwlock.h@@ -29,6 +29,8 @@ #include <linux/spinlock.h> struct percpu_rwlock { + unsigned long __percpu *reader_refcnt; + bool __percpu *writer_signal; rwlock_t global_rwlock; };
@@ -41,6 +43,8 @@ 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 af0c714..80dad93 100644
--- a/lib/percpu-rwlock.c
+++ b/lib/percpu-rwlock.c@@ -31,6 +31,17 @@ int __percpu_init_rwlock(struct percpu_rwlock *pcpu_rwlock, const char *name, struct lock_class_key *rwlock_key) { + pcpu_rwlock->reader_refcnt = alloc_percpu(unsigned long); + if (unlikely(!pcpu_rwlock->reader_refcnt)) + return -ENOMEM; + + pcpu_rwlock->writer_signal = alloc_percpu(bool); + if (unlikely(!pcpu_rwlock->writer_signal)) { + free_percpu(pcpu_rwlock->reader_refcnt); + pcpu_rwlock->reader_refcnt = NULL; + 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 +52,16 @@ int __percpu_init_rwlock(struct percpu_rwlock *pcpu_rwlock, return 0; } +void percpu_free_rwlock(struct percpu_rwlock *pcpu_rwlock) +{ + free_percpu(pcpu_rwlock->reader_refcnt); + free_percpu(pcpu_rwlock->writer_signal); + + /* Catch use-after-free bugs */ + pcpu_rwlock->reader_refcnt = NULL; + pcpu_rwlock->writer_signal = NULL; +} + void percpu_read_lock(struct percpu_rwlock *pcpu_rwlock) { read_lock(&pcpu_rwlock->global_rwlock);