Re: [PATCH] firewire: fw-core: enforce write order when updating fw_device.generation

[Nick Piggin <nickpiggin@yahoo.com.au>]

On Thursday 01 November 2007 12:49, Stefan Richter wrote:
> fw_device.node_id and fw_device.generation are accessed without mutexes.
> We have to ensure that all readers will get to see node_id updates
> before generation updates.
>

Hi, a few points:

- can change it to use spinlocks instead? This would be most
  preferable.

- if not, you need comments.

- you also seem to be missing rmb()s now. I see a couple in the
  firewire directory, but nothing that seems to be ordering loads
  of these particular fields.

- use smp_*mb() if you are just ordering regular cacheable RAM
  accesses.

Also, diffstat is a bit wrong... maybe you posted the wrong version?

> Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
> ---
>  drivers/firewire/fw-device.c   |    6 ++++++
>  drivers/firewire/fw-topology.c |    1 +
>  2 files changed, 7 insertions(+)
>
> Index: linux/drivers/firewire/fw-device.c
> ===================================================================
> --- linux.orig/drivers/firewire/fw-device.c
> +++ linux/drivers/firewire/fw-device.c
> @@ -808,6 +813,7 @@ void fw_node_event(struct fw_card *card,
>
>  		device = node->data;
>  		device->node_id = node->node_id;
> +		wmb();
>  		device->generation = card->generation;
>  		if (atomic_read(&device->state) == FW_DEVICE_RUNNING) {
>  			PREPARE_DELAYED_WORK(&device->work, fw_device_update);
> Index: linux/drivers/firewire/fw-topology.c
> ===================================================================
> --- linux.orig/drivers/firewire/fw-topology.c
> +++ linux/drivers/firewire/fw-topology.c
> @@ -518,6 +518,7 @@ fw_core_handle_bus_reset(struct fw_card
>  		card->bm_retries = 0;
>
>  	card->node_id = node_id;
> +	wmb();
>  	card->generation = generation;
>  	card->reset_jiffies = jiffies;
>  	schedule_delayed_work(&card->work, 0);