IB/srp: Make writing the add_target sysfs attr interruptible

Avoid that shutdown of srp_daemon is delayed if add_target_mutex is
held by another process.

Signed-off-by: Bart Van Assche <[e-mail]>
Signed-off-by: Doug Ledford <[e-mail]>

drivers/infiniband/ulp/srp/ib_srp.c

···
 	 */
 	scsi_host_get(target->scsi_host);
 
-	mutex_lock(&host->add_target_mutex);
+	ret = mutex_lock_interruptible(&host->add_target_mutex);
+	if (ret < 0)
+		goto put;
 
 	ret = srp_parse_options(buf, target);
 	if (ret)
···
 out:
 	mutex_unlock(&host->add_target_mutex);
 
+put:
 	scsi_host_put(target->scsi_host);
 	if (ret < 0)
 		scsi_host_put(target->scsi_host);