netdev - Re: Re: Re: [PATCH 09/11] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm

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Date:   Thu, 7 Apr 2022 22:38:13 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Jason Gunthorpe" <jgg@...pe.ca>
Cc:     "Dan Carpenter" <dan.carpenter@...cle.com>,
        linux-kernel@...r.kernel.org, chris@...kel.net, jcmvbkbc@...il.com,
        mustafa.ismail@...el.com, shiraz.saleem@...el.com,
        wg@...ndegger.com, mkl@...gutronix.de, davem@...emloft.net,
        kuba@...nel.org, pabeni@...hat.com, jes@...ined-monkey.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        alexander.deucher@....com, linux-xtensa@...ux-xtensa.org,
        linux-rdma@...r.kernel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-hippi@...site.dk,
        linux-staging@...ts.linux.dev, linux-serial@...r.kernel.org,
        linux-usb@...r.kernel.org
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.

Best regards,
Duoming Zhou