[GitHub] [incubator-nuttx] MTres19 commented on issue #2663: kthread_create hangs waiting on semaphore while trying to copy file descriptors

[GitBox <gi...@apache.org>]

MTres19 commented on issue #2663:
URL: https://github.com/apache/incubator-nuttx/issues/2663#issuecomment-757418491


   Hi @btashton yep, I think it's the semaphore for the list of open file descriptors in the task control that's being initialized. `struct tcb_s.group->tg_filelist.fl_sem`. But I'm not familiar with the code so it's hard to see the big picture... the relevant line in my driver is [here](https://github.com/MTres19/incubator-nuttx/blob/b63c54bb52f4158c6495723359032668f0947080/arch/arm/src/tiva/common/tiva_can.c#L409) if you're curious. I assume this problem hasn't come up before because most drivers wouldn't create a kernel thread in a function that's called from the application.
   
   This "fixes" the problem for me but it's just a band-aid I know.
   ~~~
   diff --git a/sched/task/task_init.c b/sched/task/task_init.c
   index b187b74ebe..3e3fd61a45 100644
   --- a/sched/task/task_init.c
   +++ b/sched/task/task_init.c
   @@ -101,11 +101,14 @@ int nxtask_init(FAR struct task_tcb_s *tcb, const char *name, int priority,
        }
    
      /* Associate file descriptors with the new task */
   -
   -  ret = group_setuptaskfiles(tcb);
   -  if (ret < 0)
   +
   +  if (!(ttype & TCB_FLAG_TTYPE_KERNEL))
        {
   -      goto errout_with_group;
   +      ret = group_setuptaskfiles(tcb);
   +      if (ret < 0)
   +        {
   +          goto errout_with_group;
   +        }
        }
    
      if (stack)
   ~~~
   
   Based on [this comment](https://github.com/apache/incubator-nuttx/blob/e772be8c8a019d4c9123bff9bc6037b4da15d946/fs/inode/fs_files.c#L155-L160).
   
   Regarding a dedicated thread vs the work queue, I actually do use the low-priority work queue to check periodically for bus errors when servicing the interrupt would be excessive. I read the admonition against using the work queue for things like this [on the wiki](https://cwiki.apache.org/confluence/display/NUTTX/Work+Queue+Deadlocks).


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