blkcg_gq->refcnt is an atomic_t. This was due to the following two
reasons.
* When blkcg_gq was added, the percpu memory allocator didn't support
allocations from !GFP_KERNEL contexts. Because blkcg_gq's are
created from IO issue paths, it couldn't use GFP_KERNEL allocations.
* A blkcg_gq represents the connection between a cgroup and a
request_queue. Because a in-flight bio already pins both, blkcg_gq
didn't usually need explicit pinning, making the use of atomic_t
acceptable albeit restrictive and fragile.
Now that the percpu allocator supports !GFP_KERNEL allocations,
there's no reason to keep using atomic_t refcnt. This will allow
clean separation between bio and request layers helping blkcg support
in blk-mq.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
block/blk-cgroup.c | 21 ++++++++++++++++-----
include/linux/blk-cgroup.h | 13 ++++---------
2 files changed, 20 insertions(+), 14 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 6482be5..60a4486 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -78,6 +78,7 @@ static void blkg_free(struct blkcg_gq *blkg)
blkg_rwstat_exit(&blkg->stat_ios);
blkg_rwstat_exit(&blkg->stat_bytes);
+ percpu_ref_exit(&blkg->refcnt);
kfree(blkg);
}
@@ -89,7 +90,7 @@ static void blkg_free(struct blkcg_gq *blkg)
* Having a reference to blkg under an rcu allows accesses to only values
* local to groups like group stats and group rate limits.
*/
-void __blkg_release_rcu(struct rcu_head *rcu_head)
+static void blkg_release_rcu(struct rcu_head *rcu_head)
{
struct blkcg_gq *blkg = container_of(rcu_head, struct blkcg_gq, rcu_head);
@@ -102,7 +103,13 @@ void __blkg_release_rcu(struct rcu_head *rcu_head)
blkg_free(blkg);
}
-EXPORT_SYMBOL_GPL(__blkg_release_rcu);
+
+static void blkg_release(struct percpu_ref *refcnt)
+{
+ struct blkcg_gq *blkg = container_of(refcnt, struct blkcg_gq, refcnt);
+
+ call_rcu(&blkg->rcu_head, blkg_release_rcu);
+}
/**
* blkg_alloc - allocate a blkg
@@ -123,6 +130,11 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
if (!blkg)
return NULL;
+ if (percpu_ref_init(&blkg->refcnt, blkg_release, 0, gfp_mask)) {
+ kfree(blkg);
+ return NULL;
+ }
+
if (blkg_rwstat_init(&blkg->stat_bytes, gfp_mask) ||
blkg_rwstat_init(&blkg->stat_ios, gfp_mask))
goto err_free;
@@ -130,7 +142,6 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
blkg->q = q;
INIT_LIST_HEAD(&blkg->q_node);
blkg->blkcg = blkcg;
- atomic_set(&blkg->refcnt, 1);
/* root blkg uses @q->root_rl, init rl only for !root blkgs */
if (blkcg != &blkcg_root) {
@@ -266,7 +277,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
return blkg;
/* @blkg failed fully initialized, use the usual release path */
- blkg_put(blkg);
+ percpu_ref_kill(&blkg->refcnt);
return ERR_PTR(ret);
err_put_congested:
@@ -373,7 +384,7 @@ static void blkg_destroy(struct blkcg_gq *blkg)
* Put the reference taken at the time of creation so that when all
* queues are gone, group can be destroyed.
*/
- blkg_put(blkg);
+ percpu_ref_kill(&blkg->refcnt);
}
/**
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 8bbc371..c0d4736 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -19,7 +19,7 @@
#include <linux/seq_file.h>
#include <linux/radix-tree.h>
#include <linux/blkdev.h>
-#include <linux/atomic.h>
+#include <linux/percpu-refcount.h>
/* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */
#define BLKG_STAT_CPU_BATCH (INT_MAX / 2)
@@ -123,7 +123,7 @@ struct blkcg_gq {
struct request_list rl;
/* reference count */
- atomic_t refcnt;
+ struct percpu_ref refcnt;
/* is this blkg online? protected by both blkcg and q locks */
bool online;
@@ -355,21 +355,16 @@ static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
*/
static inline void blkg_get(struct blkcg_gq *blkg)
{
- WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0);
- atomic_inc(&blkg->refcnt);
+ percpu_ref_get(&blkg->refcnt);
}
-void __blkg_release_rcu(struct rcu_head *rcu);
-
/**
* blkg_put - put a blkg reference
* @blkg: blkg to put
*/
static inline void blkg_put(struct blkcg_gq *blkg)
{
- WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0);
- if (atomic_dec_and_test(&blkg->refcnt))
- call_rcu(&blkg->rcu_head, __blkg_release_rcu);
+ percpu_ref_put(&blkg->refcnt);
}
/**
--
2.9.5
--
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