[PATCH -fixes 5/5] drm/vmwgfx: Fix a buffer object eviction regression

[Matthew Wilcox]

On Thu, Sep 13, 2018 at 01:58:37PM +0200, Thomas Hellstrom wrote:
> Commit 4eb085e42fde ("drm/vmwgfx: Convert to new IDA API") indroduced
> an incorrect return value from the function vmw_gmrid_man_get_node(),
> when we run out if integer ids. Instead of returning 0 (meaning
> non-fatal error) we forward the ida_simple_get error code -ENOSPC.
> This causes TTM not to retry allocation after buffer eviction and
> instead return -ENOSPC to user-space.
> 
> Fix this by returning 0 when ida_simple_get() returns -ENOSPC.

Thanks.  I got confused by the convoluted code that was there before ;-(

I think this could be better though ... if ida_alloc() ever starts
returning a different errno in the future, you'll hit the same problem,
right?  So how about this ...

 	id = ida_alloc_max(&gman->gmr_ida, gman->max_gmr_ids - 1, GFP_KERNEL);
+	if (id == -ENOMEM)
+		return -ENOMEM;
+	if (id < 0)
+		return 0;
  
 	spin_lock(&gman->lock);

But I wonder ... why is -ENOMEM seen as a fatal error?  If you free up
some memory, you'll free up an ID, so the next time around you should
be able to allocate an ID.  So shouldn't this function just have
been doing this all along?

 	id = ida_alloc_max(&gman->gmr_ida, gman->max_gmr_ids - 1, GFP_KERNEL);
+	if (id < 0)
+		return 0;