If a command with a Simple task attribute is failed due to a Unit
Attention, then a subsequent command with an Ordered task attribute will
hang forever. The reason for this is that the Unit Attention status is
checked for in target_setup_cmd_from_cdb, before the call to
target_execute_cmd, which calls target_handle_task_attr, which in turn
increments dev->simple_cmds. However, transport_generic_request_failure
still calls transport_complete_task_attr, which will decrement
dev->simple_cmds. In this case, simple_cmds is now -1. So when a
command with the Ordered task attribute is sent, target_handle_task_attr
sees that dev->simple_cmds is not 0, so it decides it can't execute the
command until all the (nonexistent) Simple commands have completed.
The solution I've implemented is to move target_scsi3_ua_check, as well as
target_alua_state_check and target_check_reservation, into
target_execute_cmd, after the call to target_handle_task_attr. I believe
this is actually the correct way this should be handled. According to
SAM-4 r14, under section 5.14:
"h) if a command other than INQUIRY, REPORT LUNS, REQUEST SENSE, or NOTIFY
DATA TRANSFER DEVICE enters the enabled command state while a unit
attention condition exists for the SCSI initiator port associated with
the I_T nexus on which the command was received, the device server shall
terminate the command with a CHECK CONDITION status. The device server
shall provide sense data that reports a unit attention condition for the
SCSI initiator port that sent the command on the I_T nexus."
But according to section 8.5 and 8.6, a command which is not yet executed
because of the presence of other tasks in the task set (i.e., one for
which target_handle_task_attr returns true) would not enter the enabled
command state; it would be in the dormant command state.
target_execute_cmd would get called when a command entered the enabled
command state, and thus that is the appropriate place to check for Unit
Attenion. Similarly, though not quite as explicit, section 5.3.3 tells
us that a Reservation Conflict status has a lower precedence than a Unit
Attention, and so this would also seem to be the appropriate place to
call target_check_reservation. I'm less sure about
target_alua_state_check, since I'm not very familiar with ALUA.
Signed-off-by: Michael Cyr <mikecyr@xxxxxxxxxxxxxxxxxx>
---
drivers/target/target_core_transport.c | 41 ++++++++++++++++++++--------------
1 file changed, 24 insertions(+), 17 deletions(-)
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 6c089af..2ee5502 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1303,23 +1303,6 @@ target_setup_cmd_from_cdb(struct se_cmd *cmd, unsigned char *cdb)
trace_target_sequencer_start(cmd);
- /*
- * Check for an existing UNIT ATTENTION condition
- */
- ret = target_scsi3_ua_check(cmd);
- if (ret)
- return ret;
-
- ret = target_alua_state_check(cmd);
- if (ret)
- return ret;
-
- ret = target_check_reservation(cmd);
- if (ret) {
- cmd->scsi_status = SAM_STAT_RESERVATION_CONFLICT;
- return ret;
- }
-
ret = dev->transport->parse_cdb(cmd);
if (ret == TCM_UNSUPPORTED_SCSI_OPCODE)
pr_warn_ratelimited("%s/%s: Unsupported SCSI Opcode 0x%02x, sending CHECK_CONDITION.\n",
@@ -1865,6 +1848,8 @@ static int __transport_check_aborted_status(struct se_cmd *, int);
void target_execute_cmd(struct se_cmd *cmd)
{
+ sense_reason_t ret;
+
/*
* Determine if frontend context caller is requesting the stopping of
* this command for frontend exceptions.
@@ -1899,6 +1884,28 @@ void target_execute_cmd(struct se_cmd *cmd)
return;
}
+ /*
+ * Check for an existing UNIT ATTENTION condition
+ */
+ ret = target_scsi3_ua_check(cmd);
+ if (ret) {
+ transport_generic_request_failure(cmd, ret);
+ return;
+ }
+
+ ret = target_alua_state_check(cmd);
+ if (ret) {
+ transport_generic_request_failure(cmd, ret);
+ return;
+ }
+
+ ret = target_check_reservation(cmd);
+ if (ret) {
+ cmd->scsi_status = SAM_STAT_RESERVATION_CONFLICT;
+ transport_generic_request_failure(cmd, ret);
+ return;
+ }
+
__target_execute_cmd(cmd);
}
EXPORT_SYMBOL(target_execute_cmd);
--
2.5.0
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