rbd: make exists flag atomic
The rbd_device->exists field can be updated asynchronously, changing
from set to clear if a mapped snapshot disappears from the base
image's snapshot context.
Currently, value of the "exists" flag is only read and modified
under protection of the header semaphore, but that will change with
the next patch. Making it atomic ensures this won't be a problem
because the a the non-existence of device will be immediately known.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 9d49e5b..2846536 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -229,7 +229,7 @@
spinlock_t lock; /* queue lock */
struct rbd_image_header header;
- bool exists;
+ atomic_t exists;
struct rbd_spec *spec;
char *header_name;
@@ -751,7 +751,7 @@
goto done;
rbd_dev->mapping.read_only = true;
}
- rbd_dev->exists = true;
+ atomic_set(&rbd_dev->exists, 1);
done:
return ret;
}
@@ -1671,7 +1671,7 @@
/* Grab a reference to the snapshot context */
down_read(&rbd_dev->header_rwsem);
- if (rbd_dev->exists) {
+ if (atomic_read(&rbd_dev->exists)) {
snapc = ceph_get_snap_context(rbd_dev->header.snapc);
rbd_assert(snapc != NULL);
}
@@ -2294,6 +2294,7 @@
return NULL;
spin_lock_init(&rbd_dev->lock);
+ atomic_set(&rbd_dev->exists, 0);
INIT_LIST_HEAD(&rbd_dev->node);
INIT_LIST_HEAD(&rbd_dev->snaps);
init_rwsem(&rbd_dev->header_rwsem);
@@ -2918,7 +2919,7 @@
/* Existing snapshot not in the new snap context */
if (rbd_dev->spec->snap_id == snap->id)
- rbd_dev->exists = false;
+ atomic_set(&rbd_dev->exists, 0);
rbd_remove_snap_dev(snap);
dout("%ssnap id %llu has been removed\n",
rbd_dev->spec->snap_id == snap->id ?