[BUG] media: platform: qcom: venus: possible ABBA deadlock in venus_event_notify() and venus_helper_vb2_buf_queue()

[Jia-Ju Bai <baijiaju1990@gmail.com>]

Hello,

My static analysis tool reports a possible ABBA deadlock in the venus 
driver in Linux 5.10:

venus_event_notify()
   mutex_lock(&core->lock); --> line 37 (Lock A)
   vdec_event_notify() --> via a function pointer 
"inst->ops->event_notify(...)"
   vdec_event_change()
     mutex_lock(&inst->lock); --> line 1301 (Lock B)

venus_helper_vb2_buf_queue()
   mutex_lock(&inst->lock); --> line 1346 (Lock B)
   session_process_buf()
     venus_pm_load_scale()
       load_scale_v4() via a function pointer 
"core->pm_ops->load_scale(...)"
         mutex_lock(&core->lock); --> line 966 (Lock A)

Besides, if "core->pm_ops->load_scale(...)" is load_scale_v1():
load_scale_v1()
   load_per_type()
     mutex_lock(&core->lock); --> line 150 (Lock A)

When venus_event_notify() and venus_helper_vb2_buf_queue() are 
concurrently executed, the deadlock can occur.

I am not quite sure whether this possible deadlock is real and how to 
fix it if it is real.
Any feedback would be appreciated, thanks

Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>


Best wishes,
Jia-Ju Bai