soc: qcom: pdr: Fix the potential deadlock

In the Linux kernel, the following vulnerability has been resolved:

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.

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.

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);

Timeout error log due to deadlock:

"

PDR: tms/servreg get domain list txn wait failed: -110

PDR: service lookup for msm/adsp/sensor_pd:tms/servreg failed: -110

"

Thanks to Bjorn and Johan for letting me know that this commit also fixes

an audio regression when using the in-kernel pd-mapper as that makes it

easier to hit this race. [1]