From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonas Johansson Subject: Using a waiting MDIO does not go well with a spinlocked bridge Date: Fri, 20 Mar 2015 13:22:46 +0100 (CET) Message-ID: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII Cc: stephen@networkplumber.org, f.fainelli@gmail.com, jiri@resnulli.us, sfeldma@gmail.com, jonasj76@gmail.com To: netdev@vger.kernel.org Return-path: Received: from mail-la0-f44.google.com ([209.85.215.44]:34856 "EHLO mail-la0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751219AbbCTM1X (ORCPT ); Fri, 20 Mar 2015 08:27:23 -0400 Received: by labjg1 with SMTP id jg1so85708176lab.2 for ; Fri, 20 Mar 2015 05:27:21 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: The bridge code will sometimes hold a spinlock and the code following must therefore be atomic. If using a MDIO call which uses a wait/sleep in this contex, the kernel will not be very happy. I'm using a switch device and wants to flush its FDB when the linux bridge FDB is flushed. I've implemented some hooks for this task. In short: bridge - br_fdb_flush() & br_fdb_delete_by_port -> switchdev - switch_flush() -> dsa - slave_flush() -> mv88e6xxx - mv88_flush() So, when a bridge port is flushed via e.g. sysfs, the mv88_flush() function will at the end be called. The mv88_flush() will use MDIO calls to set the proper registers and flush the device. But, due to that the MDIO on my platform uses wait_for_completion() and a spinlock is held (in this case in brport_store()) the process will not go very well. The only possible solutions that came into my mind is: 1) Let mv88_flush() schedule a work queue to take care of the flush later on. 2) Change the MDIO implementation to use polling. 3) Dont use spinlock in bridge code. 1) Using this approach the the atomic part is missed, i.e. the switch device isn't guaranteed to be flushed after the command has been issued. And, if a FDB entry is added (atomic) to the switch device immediately after the flush command, there will not be defined if the entry will be added before or after the flush occurs. To solve this, all (FDB) operations must be added to a work queue to assure that they are executed in the right order. 2) This will result in unsued CPU cycles. 3) Havent looked into this, but probably a lot of work. Any ideas?