Any good documentation on RTNL

Any good documentation on RTNL

[Ben Greear]

I'm wondering if anyone could point me to some documentation on
the finer points of what the rtnl_lock() does?  I can't find anything
overly useful in google or the kernel docs.

For instance, can the packet rx-logic run (on other threads?) while rtnl is held?

How about tx-logic?

In particular, I'm interested to know if it is valid to have
this state:

thread 1 holds RTNL, and blocks on thread 2 due to trying to flush a work-queue.

thread 2 is processing an item on that work-queue, and the work item is sending packets
   (and blocking for up to 200ms timeout trying to flush a wifi driver's queues).

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

Re: Any good documentation on RTNL

[Ben Hutchings]

On Wed, 2012-12-12 at 15:15 -0800, Ben Greear wrote:
> I'm wondering if anyone could point me to some documentation on
> the finer points of what the rtnl_lock() does?  I can't find anything
> overly useful in google or the kernel docs.
> 
> For instance, can the packet rx-logic run (on other threads?) while rtnl is held?
>
> How about tx-logic?

rtnl_lock() is just mutex_lock() on a particular global mutex.  Since
the RX and TX paths obviously don't take such a mutex, it has no effect
on them.

All rtnetlink operations and most net device ioctls are serialised by
this mutex (it's the BKL of networking!).

> In particular, I'm interested to know if it is valid to have
> this state:
> 
> thread 1 holds RTNL, and blocks on thread 2 due to trying to flush a work-queue.
> 
> thread 2 is processing an item on that work-queue, and the work item is sending packets
>    (and blocking for up to 200ms timeout trying to flush a wifi driver's queues).

So long as the workqueue is private (if you're flushing it, I suppose it
must be) then I don't see any problem with that.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.