memblock: add assertion for zero allocation alignment

This came to light when calling memblock allocator from arc port (for
copying flattended DT).  If a "0" alignment is passed, the allocator
round_up() call incorrectly rounds up the size to 0.

round_up(num, alignto) => ((num - 1) | (alignto -1)) + 1

While the obvious allocation failure causes kernel to panic, it is better
to warn the caller to fix the code.

Tejun suggested that instead of BUG_ON(!align) - which might be
ineffective due to pending console init and such, it is better to WARN_ON,
and continue the boot with a reasonable default align.

Caller passing @SiZe need not be handled similarly as the subsequent
panic will indicate that anyhow.

Signed-off-by: Vineet Gupta <[email protected]>
Cc: Yinghai Lu <[email protected]>
Cc: Wanpeng Li <[email protected]>
Cc: Ingo Molnar <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memblock.c

@@ -771,6 +771,9 @@ static phys_addr_t __init memblock_alloc_base_nid(phys_addr_t size,
 {
 	phys_addr_t found;
 
+	if (WARN_ON(!align))
+		align = __alignof__(long long);
+
 	/* align @size to avoid excessive fragmentation on reserved array */
 	size = round_up(size, align);