iscsi-target: Fix missed wakeup race in TX thread

The sleeping code in iscsi_target_tx_thread() is susceptible to the classic
missed wakeup race:

 - TX thread finishes handle_immediate_queue() and handle_response_queue(),
   thinks both queues are empty.
 - Another thread adds a queue entry and does wake_up_process(), which does
   nothing because the TX thread is still awake.
 - TX thread does schedule_timeout() and sleeps forever.

In practice this can kill an iSCSI connection if for example an initiator
does single-threaded writes and the target misses the wakeup window when
queueing an R2T; in this case the connection will be stuck until the
initiator loses patience and does some task management operation (or kills
the connection entirely).

Fix this by converting to wait_event_interruptible(), which does not
suffer from this sort of race.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Cc: Andy Grover <agrover@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index d6ce2182e672..035c2c762537 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -3719,7 +3719,9 @@ restart:
                  */
                 iscsit_thread_check_cpumask(conn, current, 1);
 
-                schedule_timeout_interruptible(MAX_SCHEDULE_TIMEOUT);
+                wait_event_interruptible(conn->queues_wq,
+                                         !iscsit_conn_all_queues_empty(conn) ||
+                                         ts->status == ISCSI_THREAD_SET_RESET);
 
                 if ((ts->status == ISCSI_THREAD_SET_RESET) ||
                      signal_pending(current))