On Thu, Aug 14, 2008 at 06:16:32PM +1000, Herbert Xu wrote:

On Thu, Aug 14, 2008 at 07:59:07AM +0000, Jarek Poplawski wrote:

quoted

net: Change handling of the __QDISC_STATE_SCHED flag in net_tx_action().

Change handling of the __QDISC_STATE_SCHED flag in net_tx_action() to
enable proper control in dev_deactivate_queue(). Now, if this flag is
seen as unset under root_lock means a qdisc can't be netif_scheduled.


Signed-off-by: Jarek Poplawski <redacted>

Well this probably works in practice but at least on paper it
is vulnerable to live-lock if the net_tx_action side always gets
to the trylock stage and loses to the waiting side.

An aliveness flag would be the safest.

I'm not sure of your point... This patch is only to fix my yesterday's
doubt #1, and it doesn't introduce, I hope, any new live-lock
vulnerabity. So, if you mean doubt #2, there is needed a separate
patch, but I'm not sure there is a need to add a flag. I've thougt
about a counter in a Qdisc for consecutive requeues with
netif_schedule, so we could break after some limit. Of course, your
idea could be simpler and better, but if I could only see some code...

Cheers,
Jarek P.