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

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Date:   Thu, 7 Apr 2022 17:35:47 +0000
From:   "Saleem, Shiraz" <shiraz.saleem@...el.com>
To:     "duoming@....edu.cn" <duoming@....edu.cn>,
        Jason Gunthorpe <jgg@...pe.ca>
CC:     Dan Carpenter <dan.carpenter@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "chris@...kel.net" <chris@...kel.net>,
        "jcmvbkbc@...il.com" <jcmvbkbc@...il.com>,
        "Ismail, Mustafa" <mustafa.ismail@...el.com>,
        "wg@...ndegger.com" <wg@...ndegger.com>,
        "mkl@...gutronix.de" <mkl@...gutronix.de>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "jes@...ined-monkey.org" <jes@...ined-monkey.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "alexander.deucher@....com" <alexander.deucher@....com>,
        "linux-xtensa@...ux-xtensa.org" <linux-xtensa@...ux-xtensa.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-hippi@...site.dk" <linux-hippi@...site.dk>,
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Subject: RE: Re: Re: [PATCH 09/11] drivers: infiniband: hw: Fix deadlock in
 irdma_cleanup_cm_core()

> 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.