[PATCH] Fix PR119136 Printing result of function that prints itself hangs

[Thomas Koenig]

Hi Jerry,

> The attached patch fixes this by using the TRYLOCK to see if the UNIT is 
> already in use before proceeding with the I/O.  Regression tested on 
> x86_64-linux-gnu.
> 
> The idea triggered by Thomas in the PR.
> 
> OK for mainline?

Hmm... thinking about the logic, I think that

   if (TRYLOCK(&p->lock))
     {
       if (p->child_dtio == 0)
	{
	  generate_error (&dtp->common, LIBERROR_RECURSIVE_IO, NULL);
	  return;
	}
       UNLOCK(&p->lock);
     }

might be better, otherwise we would unlock a lock that we did
not acquire.

What do you think?

Best regards

	Thomas