bootmem: make ___alloc_bootmem_node_nopanic() really nopanic

In reaction to commit 99ab7b19440a ("mm: sparse: fix usemap allocation
above node descriptor section") Johannes said:
| while backporting the below patch, I realised that your fix busted
| f5bf18fa22f8 again.  The problem was not a panicking version on
| allocation failure but when the usemap size was too large such that
| goal + size > limit triggers the BUG_ON in the bootmem allocator.  So
| we need a version that passes limit ONLY if the usemap is smaller than
| the section.

after checking the code, the name of ___alloc_bootmem_node_nopanic()
does not reflect the fact.

Make bootmem really not panic.

Hope will kill bootmem sooner.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>    [3.3.x, 3.4.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/bootmem.c

@@ -710,6 +710,10 @@ again:
 	if (ptr)
 		return ptr;
 
+	/* do not panic in alloc_bootmem_bdata() */
+	if (limit && goal + size > limit)
+		limit = 0;
+
 	ptr = alloc_bootmem_bdata(pgdat->bdata, size, align, goal, limit);
 	if (ptr)
 		return ptr;