Re: [PATCH 4/5] Fix deadlock in _int_free consistency check

[Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>]

DJ Delorie wrote:
> I think the bug can be fixed by only changing the sense of the have_lock
> condition:

> -     if (!have_lock
> +     if (have_lock

Yes it could but then it's still impossible to follow the logic... The only reason
I spotted the bug was because I refactored the code. Then the bug suddenly
became very obvious. I think locking as a side effect in conditions is something
we should avoid.

So my variant or this one are reasonable ways to do it:

 if (error detected)
   {
     if (have_lock)
       /* we had the lock during the test above, so the test is valid,
          and the error we detect is valid.  */
       print error message
     else
       /* we didn't have the lock, so aquire it and repeat the test.  If
          the error is still present, fail.  */
       get lock, repeat test, maybe print error message
   }

I suppose we could also print the error once at the end:

if (error detected)
{
  bool fail = true;
  if (!have_lock)
  {
     get_lock
     fail = repeat test
     unlock
  }
  if (fail)
    print error
}

Wilco