The mapping size is changed only very infrequently, so we don't
need to take the header mutex for checking; using READ_ONCE()
is sufficient here. And it avoids having to take a mutex in the
hot path.
Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
---
drivers/block/rbd.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index db80b964d8ea..792180548e89 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -4788,13 +4788,13 @@ static void rbd_queue_workfn(struct work_struct *work)
blk_mq_start_request(rq);
- down_read(&rbd_dev->header_rwsem);
- mapping_size = rbd_dev->mapping.size;
+ mapping_size = READ_ONCE(rbd_dev->mapping.size);
if (op_type != OBJ_OP_READ) {
+ down_read(&rbd_dev->header_rwsem);
snapc = rbd_dev->header.snapc;
ceph_get_snap_context(snapc);
+ up_read(&rbd_dev->header_rwsem);
}
- up_read(&rbd_dev->header_rwsem);
if (offset + length > mapping_size) {
rbd_warn(rbd_dev, "beyond EOD (%llu~%llu > %llu)", offset,
@@ -4981,9 +4981,9 @@ static int rbd_dev_refresh(struct rbd_device *rbd_dev)
u64 mapping_size;
int ret;
- down_write(&rbd_dev->header_rwsem);
- mapping_size = rbd_dev->mapping.size;
+ mapping_size = READ_ONCE(rbd_dev->mapping.size);
+ down_write(&rbd_dev->header_rwsem);
ret = rbd_dev_header_info(rbd_dev);
if (ret)
goto out;
@@ -4999,7 +4999,7 @@ static int rbd_dev_refresh(struct rbd_device *rbd_dev)
}
rbd_assert(!rbd_is_snap(rbd_dev));
- rbd_dev->mapping.size = rbd_dev->header.image_size;
+ WRITE_ONCE(rbd_dev->mapping.size, rbd_dev->header.image_size);
out:
up_write(&rbd_dev->header_rwsem);
--
2.16.4
