raiden00pl commented on issue #6012:
URL: https://github.com/apache/nuttx/issues/6012#issuecomment-1792748162
I came back to this problem.
Why not just add critical section like suggested before (only in this
specific place):
``` C
flags = enter_critical_section(); // <<<<<<----------------
must be here
/* The descriptor is in a valid range to file descriptor... Get the
* thread-specific file list.
*/
/* And return the file pointer from the list */
ret = nxmutex_lock(&list->fl_lock);
if (ret < 0)
{
leave_critical_section(flags); // <<<<<<<<<<<-------- here
return ret;
}
*filep = &list->fl_files[fd / CONFIG_NFILE_DESCRIPTORS_PER_BLOCK]
[fd % CONFIG_NFILE_DESCRIPTORS_PER_BLOCK];
/* if f_inode is NULL, fd was closed */
if (!(*filep)->f_inode)
{
*filep = NULL;
ret = -EBADF;
}
nxmutex_unlock(&list->fl_lock);
leave_critical_section(flags); // <<<<<<<<<<<-------- here
```
If the root of the problem is a potential interrupt occurring exactly
between `nxmutex_lock()` and `nxmutex_unlock()`, then the easiest fix is to
disable the interrupts at this point (must be before `nxmutex_lock()`).
With above change the maximum execution time of my control loop drops from
8864 cycles to 4615 cycles which looks like it solves the problem.
For SMP we probably should use `spin_lock_irqxxx()` here.
rwlock would be ideal, but implementing an effective rwlock is not an easy
task and rwlock spinlock that is already upstream will lead to deadlocks on not
SMP targets.
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