target: Drop signal_pending checks after interruptible lock acquire

Once upon a time, iscsit_get_tpg() was using an un-interruptible
lock.  The signal_pending() usage was a check to allow userspace
to break out of the operation with SIGINT.

AFAICT, there's no reason why this is necessary anymore, and as
reported by Alexey can be potentially dangerous.  Also, go ahead
and drop the other two problematic cases within iscsit_access_np()
and sbc_compare_and_write() as well.

Found by Linux Driver Verification project (linuxtesting.org).
Reported-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.c

@@ -230,7 +230,7 @@ int iscsit_access_np(struct iscsi_np *np, struct iscsi_portal_group *tpg)
 	 * Here we serialize access across the TIQN+TPG Tuple.
 	 */
 	ret = down_interruptible(&tpg->np_login_sem);
-	if ((ret != 0) || signal_pending(current))
+	if (ret != 0)
 		return -1;
 
 	spin_lock_bh(&tpg->tpg_state_lock);

drivers/target/iscsi/iscsi_target_tpg.c

@@ -161,10 +161,7 @@ struct iscsi_portal_group *iscsit_get_tpg_from_np(
 int iscsit_get_tpg(
 	struct iscsi_portal_group *tpg)
 {
-	int ret;
-
-	ret = mutex_lock_interruptible(&tpg->tpg_access_lock);
-	return ((ret != 0) || signal_pending(current)) ? -1 : 0;
+	return mutex_lock_interruptible(&tpg->tpg_access_lock);
 }
 
 void iscsit_put_tpg(struct iscsi_portal_group *tpg)

drivers/target/target_core_sbc.c

@@ -568,7 +568,7 @@ sbc_compare_and_write(struct se_cmd *cmd)
 	 * comparision using SGLs at cmd->t_bidi_data_sg..
 	 */
 	rc = down_interruptible(&dev->caw_sem);
-	if ((rc != 0) || signal_pending(current)) {
+	if (rc != 0) {
 		cmd->transport_complete_callback = NULL;
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 	}