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>

1 files changed, 4 insertions, 15 deletions

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 6f0ffd702a09..1a17399fc7db 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -107,22 +107,11 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
  */
 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);
 }