[PATCH 5/9] percpu_ref: add PCPU_REF_DEAD

Tejun Heo
2014-09-23T05:56:54Z

percpu_ref will be restructured so that percpu/atomic mode switching
and reference killing are dedoupled. In preparation, add
PCPU_REF_DEAD and PCPU_REF_ATOMIC_DEAD which is OR of ATOMIC and DEAD.
For now, ATOMIC and DEAD are changed together and all PCPU_REF_ATOMIC
uses are converted to PCPU_REF_ATOMIC_DEAD without causing any
behavior changes.

BUILD_BUG_ON() is added to percpu_ref_init() so that later flag
additions don't accidentally clobber lower bits of the pointer in
percpu_ref->pcpu_count_ptr.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
---
include/linux/percpu-refcount.h | 4 +++-
lib/percpu-refcount.c | 15 +++++++++------
2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 910e5f7..24cf157 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -57,6 +57,8 @@ typedef void (percpu_ref_func_t)(struct percpu_ref *);
/* flags set in the lower bits of percpu_ref->percpu_count_ptr */
enum {
__PERCPU_REF_ATOMIC = 1LU << 0, /* operating in atomic mode */
+ __PERCPU_REF_DEAD = 1LU << 1, /* (being) killed */
+ __PERCPU_REF_ATOMIC_DEAD = __PERCPU_REF_ATOMIC | __PERCPU_REF_DEAD,
};

struct percpu_ref {
@@ -107,7 +109,7 @@ static inline bool __ref_is_percpu(struct percpu_ref *ref,
/* paired with smp_store_release() in percpu_ref_reinit() */
smp_read_barrier_depends();

- if (unlikely(percpu_ptr & __PERCPU_REF_ATOMIC))
+ if (unlikely(percpu_ptr & __PERCPU_REF_ATOMIC_DEAD))
return false;

*percpu_countp = (unsigned long __percpu *)percpu_ptr;
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 7aef590..b0b8c09 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -34,7 +34,7 @@
static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
{
return (unsigned long __percpu *)
- (ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
+ (ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);
}

/**
@@ -52,6 +52,9 @@ static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
gfp_t gfp)
{
+ BUILD_BUG_ON(__PERCPU_REF_ATOMIC_DEAD &
+ ~(__alignof__(unsigned long) - 1));
+
atomic_long_set(&ref->count, 1 + PERCPU_COUNT_BIAS);

ref->percpu_count_ptr =
@@ -80,7 +83,7 @@ void percpu_ref_exit(struct percpu_ref *ref)

if (percpu_count) {
free_percpu(percpu_count);
- ref->percpu_count_ptr = __PERCPU_REF_ATOMIC;
+ ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
}
}
EXPORT_SYMBOL_GPL(percpu_ref_exit);
@@ -145,10 +148,10 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
percpu_ref_func_t *confirm_kill)
{
- WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC,
+ WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC_DEAD,
"%s called more than once on %pf!", __func__, ref->release);

- ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
+ ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC_DEAD;
ref->confirm_switch = confirm_kill;

call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);
@@ -180,12 +183,12 @@ void percpu_ref_reinit(struct percpu_ref *ref)
* Restore per-cpu operation. smp_store_release() is paired with
* smp_read_barrier_depends() in __ref_is_percpu() and guarantees
* that the zeroing is visible to all percpu accesses which can see
- * the following __PERCPU_REF_ATOMIC clearing.
+ * the following __PERCPU_REF_ATOMIC_DEAD clearing.
*/
for_each_possible_cpu(cpu)
*per_cpu_ptr(percpu_count, cpu) = 0;

smp_store_release(&ref->percpu_count_ptr,
- ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
+ ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);
}
EXPORT_SYMBOL_GPL(percpu_ref_reinit);
--
1.9.3