Re: [PATCH] bonding: replace system timer with work queue

[Stephen Hemminger]

Andrew Morton wrote:
> On Wed, 28 Feb 2007 10:12:01 +0100 (CET) Jaroslav Kysela <perex@xxxxxxx> wrote:
>
>   
> > Hi,
> >
> > 	please, review and apply to mm tree for further testing. The patch 
> > is also available at 
> > ftp://ftp.alsa-project.org/pub/kernel-patches/bonding-workqueue.patch .
> >     
>
> Please cc netdev@xxxxxxxxxxxxxxx on net-related patches, thanks.
>
>   
> > 					Thank you,
> > 						Jaroslav
> >
> > ==================
> > bonding: replace system timer with work queue
> >
> > This patch replaces system timer with work queue in monitor functions.
> > The reason for this change is that bonding handlers calls various
> > sleeping functions from the timer handler which is not allowed.
> >     
>
> Which sleeping functions?  I'd have expected the kernel to spew runtime
> warnings when this happens, but I don't recall any such reports.
>
>
>   
> > Because we cannot share the main workqueue threads (rtnl_lock is used
> > also in linkwatch_event) - new bond workqueue thread is created.
> >
> > Signed-off-by: Jaroslav Kysela <perex@xxxxxxx>
> >
> > diff -rupN linux-2.6.20.orig/drivers/net/bonding/bond_3ad.c linux-2.6.20/drivers/net/bonding/bond_3ad.c
> > --- linux-2.6.20.orig/drivers/net/bonding/bond_3ad.c	2007-02-04 19:44:54.000000000 +0100
> > +++ linux-2.6.20/drivers/net/bonding/bond_3ad.c	2007-02-28 09:19:43.831369202 +0100
> > @@ -2097,8 +2097,10 @@ void bond_3ad_unbind_slave(struct slave 
> >   * times out, and it selects an aggregator for the ports that are yet not
> >   * related to any aggregator, and selects the active aggregator for a bond.
> >   */
> > -void bond_3ad_state_machine_handler(struct bonding *bond)
> > +void bond_3ad_state_machine_handler(struct work_struct *work)
> >  {
> > +	struct ad_bond_info *ad_info = container_of(work, struct ad_bond_info, ad_work.work);
> > +	struct bonding *bond = (struct bonding *)((char *)ad_info - offsetof(struct bonding, ad_info));
> >     
>
> We can use containers_of here too?
>
>   
> > -void bond_alb_monitor(struct bonding *bond)
> > +void bond_alb_monitor(struct work_struct *work)
> >  {
> > -	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
> > +	struct alb_bond_info *bond_info = container_of(work, struct alb_bond_info, alb_work.work);
> > +	struct bonding *bond = (struct bonding *)((char *)bond_info - offsetof(struct bonding, alb_info));
> >     
>
> And here.
>
>   
> > +		cancel_rearming_delayed_workqueue(bond_wq, &(BOND_AD_INFO(bond).ad_work));
> >     

As I mentioned earlier this call to cancel_rearming_delayed_workqueue 
can deadlock
with netlink_watch. This happens if:

dev_close
   rtnl_lock                     carrier lost on device
   bond_close                 netlink related workqueue event waiting 
for rtnl
      cancel_workqueue
         spinning waiting for workq to drain

The agreed upon semantics is to never do any operation that waits for workq
to drain with RTNL held.

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