On Mon 18-02-19 18:48:14, Mike Rapoport wrote:
> On Mon, Feb 18, 2019 at 04:22:13PM +0100, Michal Hocko wrote:
[...]
> > Thinking about it some more, is it possible that we are overflowing by 1
> > here?
>
> Looks like that, the end_pfn is actually the first pfn in the next section.
Thanks for the confirmation. I guess it also exaplains why nobody has
noticed this off-by-one. Most people seem to use VMEMMAP SPARSE model
and we are safe there.
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 124e794867c5..6618b9d3e53a 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1234,10 +1234,10 @@ bool is_mem_section_removable(unsigned long
> > start_pfn, unsigned long nr_pages)
> > {
> > struct page *page = pfn_to_page(start_pfn);
> > unsigned long end_pfn = min(start_pfn + nr_pages,
> > zone_end_pfn(page_zone(page)));
> > - struct page *end_page = pfn_to_page(end_pfn);
> > + struct page *end_page = pfn_to_page(end_pfn - 1);
> >
> > /* Check the starting page of each pageblock within the range */
> > - for (; page < end_page; page = next_active_pageblock(page)) {
> > + for (; page <= end_page; page = next_active_pageblock(page)) {
> > if (!is_pageblock_removable_nolock(page))
> > return false;
> > cond_resched();
>
> Works with your fix, but I think mine is more intuitive ;-)
I would rather go and rework this to pfns. What about this instead.
Slightly larger but arguably cleared code?
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 124e794867c5..a799a0bdbf34 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1188,11 +1188,13 @@ static inline int pageblock_free(struct page *page)
return PageBuddy(page) && page_order(page) >= pageblock_order;
}
-/* Return the start of the next active pageblock after a given page */
-static struct page *next_active_pageblock(struct page *page)
+/* Return the pfn of the start of the next active pageblock after a given pfn
*/
+static unsigned long next_active_pageblock(unsigned long pfn)
{
+ struct page *page = pfn_to_page(pfn);
+
/* Ensure the starting page is pageblock-aligned */
- BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1));
+ BUG_ON(pfn & (pageblock_nr_pages - 1));
/* If the entire pageblock is free, move to the end of free page */
if (pageblock_free(page)) {
@@ -1200,16 +1202,16 @@ static struct page *next_active_pageblock(struct page
*page)
/* be careful. we don't have locks, page_order can be changed.*/
order = page_order(page);
if ((order < MAX_ORDER) && (order >= pageblock_order))
- return page + (1 << order);
+ return pfn + (1 << order);
}
- return page + pageblock_nr_pages;
+ return pfn + pageblock_nr_pages;
}
-static bool is_pageblock_removable_nolock(struct page *page)
+static bool is_pageblock_removable_nolock(unsigned long pfn)
{
+ struct page *page = pfn_to_page(pfn);
struct zone *zone;
- unsigned long pfn;
/*
* We have to be careful here because we are iterating over memory
@@ -1232,13 +1234,14 @@ static bool is_pageblock_removable_nolock(struct page
*page)
/* Checks if this range of memory is likely to be hot-removable. */
bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
{
- struct page *page = pfn_to_page(start_pfn);
- unsigned long end_pfn = min(start_pfn + nr_pages,
zone_end_pfn(page_zone(page)));
- struct page *end_page = pfn_to_page(end_pfn);
+ unsigned long end_pfn;
+
+ end_pfn = min(start_pfn + nr_pages,
+ zone_end_pfn(page_zone(pfn_to_page(start_pfn))));
/* Check the starting page of each pageblock within the range */
- for (; page < end_page; page = next_active_pageblock(page)) {
- if (!is_pageblock_removable_nolock(page))
+ for (; start_pfn < end_pfn; start_pfn =
next_active_pageblock(start_pfn)) {
+ if (!is_pageblock_removable_nolock(start_pfn))
return false;
cond_resched();
}
--
Michal Hocko
SUSE Labs
