percpu-refcount: Don't use silly cmpxchg()
The cmpxchg() was just to ensure the debug check didn't race, which was
a bit excessive. The caller is supposed to do the appropriate
synchronization, which means percpu_ref_kill() can just do a simple
store.
Signed-off-by: Kent Overstreet <koverstreet@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 6f0ffd7..1a17399f 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -107,22 +107,11 @@
*/
void percpu_ref_kill(struct percpu_ref *ref)
{
- unsigned __percpu *pcpu_count, *old, *new;
+ WARN_ONCE(REF_STATUS(ref->pcpu_count) == PCPU_REF_DEAD,
+ "percpu_ref_kill() called more than once!\n");
- pcpu_count = ACCESS_ONCE(ref->pcpu_count);
-
- do {
- if (REF_STATUS(pcpu_count) == PCPU_REF_DEAD) {
- WARN(1, "percpu_ref_kill() called more than once!\n");
- return;
- }
-
- old = pcpu_count;
- new = (unsigned __percpu *)
- (((unsigned long) pcpu_count)|PCPU_REF_DEAD);
-
- pcpu_count = cmpxchg(&ref->pcpu_count, old, new);
- } while (pcpu_count != old);
+ ref->pcpu_count = (unsigned __percpu *)
+ (((unsigned long) ref->pcpu_count)|PCPU_REF_DEAD);
call_rcu(&ref->rcu, percpu_ref_kill_rcu);
}