drbd: fix potential deadlock when trying to detach during handshake

When requesting a detach, we first suspend IO, and also inhibit meta-data IO
by means of drbd_md_get_buffer(), because we don't want to "fail" the disk
while there is IO in-flight: the transition into D_FAILED for detach purposes
may get misinterpreted as actual IO error in a confused endio function.

We wrap it all into wait_event(), to retry in case the drbd_req_state()
returns SS_IN_TRANSIENT_STATE, as it does for example during an ongoing
connection handshake.

In that example, the receiver thread may need to grab drbd_md_get_buffer()
during the handshake to make progress.  To avoid potential deadlock with
detach, detach needs to grab and release the meta data buffer inside of
that wait_event retry loop. To avoid lock inversion between
mutex_lock(&device->state_mutex) and drbd_md_get_buffer(device),
introduce a new enum chg_state_flag CS_INHIBIT_MD_IO, and move the
call to drbd_md_get_buffer() inside the state_mutex grabbed in
drbd_req_state().

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 8 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_state.h b/drivers/block/drbd/drbd_state.h
index 6c9d5d4a8a75..0276c98fbbdd 100644
--- a/drivers/block/drbd/drbd_state.h
+++ b/drivers/block/drbd/drbd_state.h
@@ -71,6 +71,10 @@ enum chg_state_flags {
 	CS_DC_SUSP       = 1 << 10,
 	CS_DC_MASK       = CS_DC_ROLE + CS_DC_PEER + CS_DC_CONN + CS_DC_DISK + CS_DC_PDSK,
 	CS_IGN_OUTD_FAIL = 1 << 11,
+
+	/* Make sure no meta data IO is in flight, by calling
+	 * drbd_md_get_buffer().  Used for graceful detach. */
+	CS_INHIBIT_MD_IO = 1 << 12,
 };
 
 /* drbd_dev_state and drbd_state are different types. This is to stress the
@@ -156,6 +160,10 @@ static inline int drbd_request_state(struct drbd_device *device,
 	return _drbd_request_state(device, mask, val, CS_VERBOSE + CS_ORDERED);
 }
 
+/* for use in adm_detach() (drbd_adm_detach(), drbd_adm_down()) */
+enum drbd_state_rv
+drbd_request_detach_interruptible(struct drbd_device *device);
+
 enum drbd_role conn_highest_role(struct drbd_connection *connection);
 enum drbd_role conn_highest_peer(struct drbd_connection *connection);
 enum drbd_disk_state conn_highest_disk(struct drbd_connection *connection);