Re: [PATCH -next] mm/hotplug: silence a lockdep splat with printk()

[Qian Cai]

> On Jan 14, 2020, at 8:19 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> On Tue, 14 Jan 2020 20:02:31 -0500 Qian Cai <cai@xxxxxx> wrote:
> 
>> 
>> 
>>>> @@ -8290,8 +8290,10 @@ bool has_unmovable_pages(struct zone *zo
>>>> 	return false;
>>>> unmovable:
>>>> 	WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
>>>> -	if (flags & REPORT_FAILURE)
>>>> -		dump_page(pfn_to_page(pfn + iter), reason);
>>>> +	if (flags & REPORT_FAILURE) {
>>>> +		page = pfn_to_page(pfn + iter);
>>> 
>>> This statement appears to be unnecessary.
>> 
>> dump_page() in set_migratetype_isolate() needs that âpageâ.
> 
> local var `page' is never used after this statement.
> 

The goal is to reuse the parameter of has_unmovable_pages((â, page, â)
as a return value, so after it returns, dump_page(page, ...) could use it. I
donât see where it was defined as a local variable.

This is probably a bit too hacky, so Iâll change has_unmovable_pages()
to either return "struct page *â or NULL which is easier to understand.