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

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Message-Id: <20250128080751.3718762-1-mukesh.ojha@oss.qualcomm.com>
Date: Tue, 28 Jan 2025 13:37:51 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: andersson@...nel.org, konradybcio@...nel.org
Cc: linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mukesh Ojha <mukesh.ojha@....qualcomm.com>,
        Saranya R <quic_sarar@...cinc.com>
Subject: [PATCH] soc: qcom: pdr: Fix the potential deadlock

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>
---
 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