RE: Re: Re: [PATCH 09/11] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core()

[Saleem, Shiraz]

> Subject: Re: Re: Re: [PATCH 09/11] drivers: infiniband: hw: Fix deadlock in
> irdma_cleanup_cm_core()
> 
> Hello,
> 
> On Thu, 7 Apr 2022 11:23:55 -0300 Jason Gunthorpe wrote:
> 
> > > > > diff --git a/drivers/infiniband/hw/irdma/cm.c
> > > > > b/drivers/infiniband/hw/irdma/cm.c
> > > > > index dedb3b7edd8..019dd8bfe08 100644
> > > > > +++ b/drivers/infiniband/hw/irdma/cm.c
> > > > > @@ -3252,8 +3252,11 @@ void irdma_cleanup_cm_core(struct
> irdma_cm_core *cm_core)
> > > > >  		return;
> > > > >
> > > > >  	spin_lock_irqsave(&cm_core->ht_lock, flags);
> > > > > -	if (timer_pending(&cm_core->tcp_timer))
> > > > > +	if (timer_pending(&cm_core->tcp_timer)) {
> > > > > +		spin_unlock_irqrestore(&cm_core->ht_lock, flags);
> > > > >  		del_timer_sync(&cm_core->tcp_timer);
> > > > > +		spin_lock_irqsave(&cm_core->ht_lock, flags);
> > > > > +	}
> > > > >  	spin_unlock_irqrestore(&cm_core->ht_lock, flags);
> > > >
> > > > This lock doesn't seem to be protecting anything.  Also do we need
> > > > to check timer_pending()?  I think the del_timer_sync() function
> > > > will just return directly if there isn't a pending lock?
> > >
> > > Thanks a lot for your advice, I will remove the timer_pending() and
> > > the redundant lock.
> >
> > Does del_timer_sync work with a self-rescheduling timer like this has?
> 
> The del_timer_sync() will kill the timer although it is self-rescheduling.
> We could use other functions to arouse timer again besides timer handler itself.
> 

By the time we execute, irdma_cleanup_cm_core all cm_nodes should be culled and there will be no timer add from the timer handler.

And the secondary path to add timer, irdma_schedule_timer is guaranteed to not run.