5.4-stable review patch. If anyone has any objections, please let me know.
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From: Ilya Dryomov idryomov@gmail.com
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@vger.kernel.org # 0b035401c570: rbd: move rbd_dev_refresh() definition Cc: stable@vger.kernel.org # 510a7330c82a: rbd: decouple header read-in from updating rbd_dev->header Cc: stable@vger.kernel.org # c10311776f0a: rbd: decouple parent info read-in from updating rbd_dev Cc: stable@vger.kernel.org Fixes: 870611e4877e ("rbd: get snapshot context after exclusive lock is ensured to be held") Signed-off-by: Ilya Dryomov idryomov@gmail.com Reviewed-by: Dongsheng Yang dongsheng.yang@easystack.cn [idryomov@gmail.com: backport to 5.4: open-code rbd_is_snap(), preserve rbd_exists_validate() call] Signed-off-by: Sasha Levin sashal@kernel.org --- 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 e86dca49fae71..7117fa4902435 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;