target: Allow Write Exclusive non-reservation holders to READ

commit 1ecc7586 upstream.

For PGR reservation of type Write Exclusive Access, allow all non
reservation holding I_T nexuses with active registrations to READ
from the device.

This addresses a bug where active registrations that attempted
to READ would result in an reservation conflict.
Signed-off-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/target/target_core_pr.c

@@ -526,6 +526,18 @@ static int core_scsi3_pr_seq_non_holder(
 				" reservation\n", cdb[0],
 				core_scsi3_pr_dump_type(pr_reg_type));
 
+			return 0;
+		}
+       } else if (we && registered_nexus) {
+               /*
+                * Reads are allowed for Write Exclusive locks
+                * from all registrants.
+                */
+               if (cmd->data_direction == DMA_FROM_DEVICE) {
+                       pr_debug("Allowing READ CDB: 0x%02x for %s"
+                               " reservation\n", cdb[0],
+                               core_scsi3_pr_dump_type(pr_reg_type));
+
                        return 0;
                }
 	}