linux-kernel - Re: [PATCH v2] soc: qcom: pdr: Fix the potential deadlock

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Message-ID: <Z6nE0kxF2ipItB2r@hu-mojha-hyd.qualcomm.com>
Date: Mon, 10 Feb 2025 14:50:18 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: konradybcio@...nel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Saranya R <quic_sarar@...cinc.com>, Johan Hovold <johan@...nel.org>,
        Frank Oltmanns <frank@...manns.dev>
Subject: Re: [PATCH v2] soc: qcom: pdr: Fix the potential deadlock

On Thu, Feb 06, 2025 at 04:13:25PM -0600, Bjorn Andersson wrote:

> On Wed, Jan 29, 2025 at 09:25:44PM +0530, Mukesh Ojha wrote:
> > When some client process A call pdr_add_lookup() to add the look up for
> > the service and does schedule locator work, later a process B got a new
> > server packet indicating locator is up and call pdr_locator_new_server()
> > which eventually sets pdr->locator_init_complete to true which process A
> > sees and takes list lock and queries domain list but it will timeout due
> > to deadlock as the response will queued to the same qmi->wq and it is
> > ordered workqueue and process B is not able to complete new server
> > request work due to deadlock on list lock.
> > 
> >        Process A                        Process B
> > 
> >                                      process_scheduled_works()
> > pdr_add_lookup()                      qmi_data_ready_work()
> >  process_scheduled_works()             pdr_locator_new_server()
> >                                          pdr->locator_init_complete=true;
> >    pdr_locator_work()
> >     mutex_lock(&pdr->list_lock);
> > 
> >      pdr_locate_service()                  mutex_lock(&pdr->list_lock);
> > 
> >       pdr_get_domain_list()
> >        pr_err("PDR: %s get domain list
> >                txn wait failed: %d\n",
> >                req->service_name,
> >                ret);
> > 
> > Fix it by removing the unnecessary list iteration as the list iteration
> > is already being done inside locator work, so avoid it here and just
> > call schedule_work() here.
> > 
> 
> I came to the same patch while looking into the issue related to
> in-kernel pd-mapper reported here:
> https://lore.kernel.org/lkml/Zqet8iInnDhnxkT9@hovoldconsulting.com/
> 
> So:
> Reviewed-by: Bjorn Andersson <bjorn.andersson@....qualcomm.com>
> Tested-by: Bjorn Andersson <bjorn.andersson@....qualcomm.com>

Thanks.,

> 
> > Fixes: fbe639b44a82 ("soc: qcom: Introduce Protection Domain Restart helpers")
> > CC: stable@...r.kernel.org
> > Signed-off-by: Saranya R <quic_sarar@...cinc.com>
> 
> Can we please use full names?

I have informed her about this and she wants the same name to be mentioned here as well.
> 
> > Signed-off-by: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
> 
> Unfortunately I can't merge this; Saranya's S-o-b comes first which
> implies that she authored the patch, but you're listed as author.

I will correct it.

-Mukesh

> 
> Regards,
> Bjorn
> 
> > ---
> > Changes in v2:
> >  - Added Fixes tag,
> > 
> >  drivers/soc/qcom/pdr_interface.c | 8 +-------
> >  1 file changed, 1 insertion(+), 7 deletions(-)
> > 
> > diff --git a/drivers/soc/qcom/pdr_interface.c b/drivers/soc/qcom/pdr_interface.c
> > index 328b6153b2be..71be378d2e43 100644
> > --- a/drivers/soc/qcom/pdr_interface.c
> > +++ b/drivers/soc/qcom/pdr_interface.c
> > @@ -75,7 +75,6 @@ static int pdr_locator_new_server(struct qmi_handle *qmi,
> >  {
> >  	struct pdr_handle *pdr = container_of(qmi, struct pdr_handle,
> >  					      locator_hdl);
> > -	struct pdr_service *pds;
> >  
> >  	mutex_lock(&pdr->lock);
> >  	/* Create a local client port for QMI communication */
> > @@ -87,12 +86,7 @@ static int pdr_locator_new_server(struct qmi_handle *qmi,
> >  	mutex_unlock(&pdr->lock);
> >  
> >  	/* Service pending lookup requests */
> > -	mutex_lock(&pdr->list_lock);
> > -	list_for_each_entry(pds, &pdr->lookups, node) {
> > -		if (pds->need_locator_lookup)
> > -			schedule_work(&pdr->locator_work);
> > -	}
> > -	mutex_unlock(&pdr->list_lock);
> > +	schedule_work(&pdr->locator_work);
> >  
> >  	return 0;
> >  }
> > -- 
> > 2.34.1
> >