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Subject[PATCH 2/4] Adds an RCU-protected pointer to request_queue that makes it easy to
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find the gendisk that the queue manages.
---
block/blk-cgroup.c | 10 ++++++----
block/blk-sysfs.c | 4 ++++
include/linux/blkdev.h | 6 ++++++
3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 917957d..809451f 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -179,16 +179,18 @@ static int blkiocg_##__VAR##_read(struct cgroup *cgroup, \
struct blkio_cgroup *blkcg; \
struct blkio_group *blkg; \
struct hlist_node *n; \
+ struct gendisk *disk; \
\
if (!cgroup_lock_live_group(cgroup)) \
return -ENODEV; \
\
blkcg = cgroup_to_blkio_cgroup(cgroup); \
rcu_read_lock(); \
- hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) {\
- if (blkg->dev) \
- seq_printf(m, "%u:%u %lu\n", MAJOR(blkg->dev), \
- MINOR(blkg->dev), blkg->__VAR); \
+ hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) { \
+ disk = rcu_dereference(blkg->queue->disk); \
+ if (disk) \
+ seq_printf(m, "%s %lu\n", disk->disk_name, \
+ blkg->__VAR); \
} \
rcu_read_unlock(); \
cgroup_unlock(); \
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 2ae2cb3..14cab6a 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -484,6 +484,8 @@ int blk_register_queue(struct gendisk *disk)
if (!q->request_fn)
return 0;

+ rcu_assign_pointer(q->disk, disk);
+
ret = elv_register_queue(q);
if (ret) {
kobject_uevent(&q->kobj, KOBJ_REMOVE);
@@ -505,6 +507,8 @@ void blk_unregister_queue(struct gendisk *disk)
if (q->request_fn)
elv_unregister_queue(q);

+ rcu_assign_pointer(q->disk, NULL);
+
kobject_uevent(&q->kobj, KOBJ_REMOVE);
kobject_del(&q->kobj);
blk_trace_remove_sysfs(disk_to_dev(disk));
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ebd22db..e531cf2 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -441,6 +441,12 @@ struct request_queue
#if defined(CONFIG_BLK_DEV_BSG)
struct bsg_class_device bsg_dev;
#endif
+
+ /*
+ * an RCU-protected pointer that can be NULL when devices are
+ * removed
+ */
+ struct gendisk *disk;
};

#define QUEUE_FLAG_CLUSTER 0 /* cluster several segments into 1 */


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