On 15-10-12 07:52 PM, Scott Feldman wrote:
> On Mon, Oct 12, 2015 at 11:03 AM, Jiri Pirko <j...@resnulli.us> wrote:
>> From: Jiri Pirko <j...@mellanox.com>
>>
>> Caller should know if he can call attr_set directly (when holding RTNL)
>> or if he has to defer the att_set processing for later.
>>
>> This also allows drivers to sleep inside attr_set and report operation
>> status back to switchdev core. Switchdev core then warns if status is
>> not ok, instead of silent errors happening in drivers.
>>
>> Signed-off-by: Jiri Pirko <j...@mellanox.com>
>> ---
>> include/net/switchdev.h | 1 +
>> net/bridge/br_stp.c | 3 +-
>> net/switchdev/switchdev.c | 107
>> ++++++++++++++++++++++++----------------------
>> 3 files changed, 59 insertions(+), 52 deletions(-)
>>
>> diff --git a/include/net/switchdev.h b/include/net/switchdev.h
>> index d2879f2..6b109e4 100644
>> --- a/include/net/switchdev.h
>> +++ b/include/net/switchdev.h
>> @@ -17,6 +17,7 @@
>>
>> #define SWITCHDEV_F_NO_RECURSE BIT(0)
>> #define SWITCHDEV_F_SKIP_EOPNOTSUPP BIT(1)
>> +#define SWITCHDEV_F_DEFER BIT(2)
>>
>> struct switchdev_trans_item {
>> struct list_head list;
>> diff --git a/net/bridge/br_stp.c b/net/bridge/br_stp.c
>> index db6d243de..80c34d7 100644
>> --- a/net/bridge/br_stp.c
>> +++ b/net/bridge/br_stp.c
>> @@ -41,13 +41,14 @@ void br_set_state(struct net_bridge_port *p, unsigned
>> int state)
>> {
>> struct switchdev_attr attr = {
>> .id = SWITCHDEV_ATTR_ID_PORT_STP_STATE,
>> + .flags = SWITCHDEV_F_DEFER,
>> .u.stp_state = state,
>> };
>> int err;
>>
>> p->state = state;
>> err = switchdev_port_attr_set(p->dev, &attr);
>> - if (err && err != -EOPNOTSUPP)
>> + if (err)
>
> This looks like a problem as now all other non-switchdev ports will
> get an WARN in the log when STP state changes. We should only WARN if
> there was an err and the err is not -EOPNOTSUPP.
>
>> br_warn(p->br, "error setting offload STP state on port
>> %u(%s)\n",
>> (unsigned int) p->port_no, p->dev->name);
>> }
>
> <snip>
>
>> struct switchdev_attr_set_work {
>> struct work_struct work;
>> struct net_device *dev;
>> @@ -183,14 +226,17 @@ static void switchdev_port_attr_set_work(struct
>> work_struct *work)
>> {
>> struct switchdev_attr_set_work *asw =
>> container_of(work, struct switchdev_attr_set_work, work);
>> + bool rtnl_locked = rtnl_is_locked();
>> int err;
>>
>> - rtnl_lock();
>> - err = switchdev_port_attr_set(asw->dev, &asw->attr);
>> + if (!rtnl_locked)
>> + rtnl_lock();
>
> I'm not following this change. If someone else has rtnl_lock, we'll
> not wait to grab it here ourselves, and proceed as if we have the
> lock. But what if that someone else releases the lock in the middle
> of us doing switchdev_port_attr_set_now? Seems we want to
> unconditionally wait and grab the lock. We need to block anything
> from moving while we do the attr set.
>
Also an additional race between setting rtnl_locked and the if stmt
and then grabbing the lock. There seems to be a something of pattern
around this where other subsystems use a rtnl_trylock and if it fails
do a restart/re-queue operation to retry. Looks like how you handle
it in the team driver at least.
>> + err = switchdev_port_attr_set_now(asw->dev, &asw->attr);
>> if (err && err != -EOPNOTSUPP)
>> netdev_err(asw->dev, "failed (err=%d) to set attribute
>> (id=%d)\n",
>> err, asw->attr.id);
>> - rtnl_unlock();
>> + if (!rtnl_locked)
>> + rtnl_unlock();
>>
>> dev_put(asw->dev);
>> kfree(work);
>> @@ -211,7 +257,7 @@ static int switchdev_port_attr_set_defer(struct
>> net_device *dev,
>> asw->dev = dev;
>> memcpy(&asw->attr, attr, sizeof(asw->attr));
>>
>> - schedule_work(&asw->work);
>> + queue_work(switchdev_wq, &asw->work);
>>
>> return 0;
>> }
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