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

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Message-ID: <Z5pNdXzj04tEroYS@hu-mojha-hyd.qualcomm.com>
Date: Wed, 29 Jan 2025 21:17:01 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: andersson@...nel.org, konradybcio@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Saranya R <quic_sarar@...cinc.com>
Subject: Re: [PATCH] soc: qcom: pdr: Fix the potential deadlock

On Tue, Jan 28, 2025 at 06:10:24PM +0200, Dmitry Baryshkov wrote:
> On Tue, Jan 28, 2025 at 01:37:51PM +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.
> > 
> > Signed-off-by: Saranya R <quic_sarar@...cinc.com>
> > Signed-off-by: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
> 
> Missing Fixes tag.

Sure, will add.

-Mukesh
> 
> > ---
> >  drivers/soc/qcom/pdr_interface.c | 8 +-------
> >  1 file changed, 1 insertion(+), 7 deletions(-)
> > 
> 
> -- 
> With best wishes
> Dmitry