commit 0b207d02bd9ab8dcc31b262ca9f60dbc1822500d upstream.
rbd_dev_refresh() has been holding header_rwsem across header and
parent info read-in unnecessarily for ages. With commit 870611e4877e
("rbd: get snapshot context after exclusive lock is ensured to be
held"), the potential for deadlocks became much more real owning to
a) header_rwsem now nesting inside lock_rwsem and b) rw_semaphores
not allowing new readers after a writer is registered.
For example, assuming that I/O request 1, I/O request 2 and header
read-in request all target the same OSD:
1. I/O request 1 comes in and gets submitted
2. watch error occurs
3. rbd_watch_errcb() takes lock_rwsem for write, clears owner_cid and
releases lock_rwsem
4. after reestablishing the watch, rbd_reregister_watch() calls
rbd_dev_refresh() which takes header_rwsem for write and submits
a header read-in request
5. I/O request 2 comes in: after taking lock_rwsem for read in
__rbd_img_handle_request(), it blocks trying to take header_rwsem
for read in rbd_img_object_requests()
6. another watch error occurs
7. rbd_watch_errcb() blocks trying to take lock_rwsem for write
8. I/O request 1 completion is received by the messenger but can't be
processed because lock_rwsem won't be granted anymore
9. header read-in request completion can't be received, let alone
processed, because the messenger is stranded
Change rbd_dev_refresh() to take header_rwsem only for actually
updating rbd_dev->header. Header and parent info read-in don't need
any locking.
Cc: stable@xxxxxxxxxxxxxxx # 0b035401c570: rbd: move rbd_dev_refresh() definition
Cc: stable@xxxxxxxxxxxxxxx # 510a7330c82a: rbd: decouple header read-in from updating rbd_dev->header
Cc: stable@xxxxxxxxxxxxxxx # c10311776f0a: rbd: decouple parent info read-in from updating rbd_dev
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 870611e4877e ("rbd: get snapshot context after exclusive lock is ensured to be held")
Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Reviewed-by: Dongsheng Yang <dongsheng.yang@xxxxxxxxxxxx>
[idryomov@xxxxxxxxx: backport to 5.4: open-code rbd_is_snap(), preserve
rbd_exists_validate() call]
---
drivers/block/rbd.c | 31 ++++++++++++++++---------------
1 file changed, 16 insertions(+), 15 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index e86dca49fae7..7117fa490243 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -7001,7 +7001,19 @@ static void rbd_dev_update_header(struct rbd_device *rbd_dev,
rbd_assert(rbd_image_format_valid(rbd_dev->image_format));
rbd_assert(rbd_dev->header.object_prefix); /* !first_time */
- rbd_dev->header.image_size = header->image_size;
+ if (rbd_dev->header.image_size != header->image_size) {
+ rbd_dev->header.image_size = header->image_size;
+
+ if (rbd_dev->spec->snap_id == CEPH_NOSNAP) {
+ rbd_dev->mapping.size = header->image_size;
+ rbd_dev_update_size(rbd_dev);
+ }
+ }
+
+ if (rbd_dev->spec->snap_id != CEPH_NOSNAP) {
+ /* validate mapped snapshot's EXISTS flag */
+ rbd_exists_validate(rbd_dev);
+ }
ceph_put_snap_context(rbd_dev->header.snapc);
rbd_dev->header.snapc = header->snapc;
@@ -7059,11 +7071,9 @@ static int rbd_dev_refresh(struct rbd_device *rbd_dev)
{
struct rbd_image_header header = { 0 };
struct parent_image_info pii = { 0 };
- u64 mapping_size;
int ret;
- down_write(&rbd_dev->header_rwsem);
- mapping_size = rbd_dev->mapping.size;
+ dout("%s rbd_dev %p\n", __func__, rbd_dev);
ret = rbd_dev_header_info(rbd_dev, &header, false);
if (ret)
@@ -7079,22 +7089,13 @@ static int rbd_dev_refresh(struct rbd_device *rbd_dev)
goto out;
}
+ down_write(&rbd_dev->header_rwsem);
rbd_dev_update_header(rbd_dev, &header);
if (rbd_dev->parent)
rbd_dev_update_parent(rbd_dev, &pii);
-
- if (rbd_dev->spec->snap_id == CEPH_NOSNAP) {
- rbd_dev->mapping.size = rbd_dev->header.image_size;
- } else {
- /* validate mapped snapshot's EXISTS flag */
- rbd_exists_validate(rbd_dev);
- }
-
-out:
up_write(&rbd_dev->header_rwsem);
- if (!ret && mapping_size != rbd_dev->mapping.size)
- rbd_dev_update_size(rbd_dev);
+out:
rbd_parent_info_cleanup(&pii);
rbd_image_header_cleanup(&header);
return ret;
--
2.41.0
