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

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Date:   Thu, 7 Apr 2022 11:23:55 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     duoming@....edu.cn
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: [PATCH 09/11] drivers: infiniband: hw: Fix deadlock in
 irdma_cleanup_cm_core()

On Thu, Apr 07, 2022 at 08:54:13PM +0800, duoming@....edu.cn 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?

Jason