mm, memory_hotplug: is_mem_section_removable do not pass the end of a…

… zone

Patch series "mm, memory_hotplug: fix uninitialized pages fallouts", v2.

Mikhail Zaslonko has posted fixes for the two bugs quite some time ago
[1].  I have pushed back on those fixes because I believed that it is
much better to plug the problem at the initialization time rather than
play whack-a-mole all over the hotplug code and find all the places
which expect the full memory section to be initialized.

We have ended up with commit 2830bf6 ("mm, memory_hotplug:
initialize struct pages for the full memory section") merged and cause a
regression [2][3].  The reason is that there might be memory layouts
when two NUMA nodes share the same memory section so the merged fix is
simply incorrect.

In order to plug this hole we really have to be zone range aware in
those handlers.  I have split up the original patch into two.  One is
unchanged (patch 2) and I took a different approach for `removable'
crash.

[1] http://lkml.kernel.org/r/[email protected]
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1666948
[3] http://lkml.kernel.org/r/[email protected]

This patch (of 2):

Mikhail has reported the following VM_BUG_ON triggered when reading sysfs
removable state of a memory block:

 page:000003d08300c000 is uninitialized and poisoned
 page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
 Call Trace:
   is_mem_section_removable+0xb4/0x190
   show_mem_removable+0x9a/0xd8
   dev_attr_show+0x34/0x70
   sysfs_kf_seq_show+0xc8/0x148
   seq_read+0x204/0x480
   __vfs_read+0x32/0x178
   vfs_read+0x82/0x138
   ksys_read+0x5a/0xb0
   system_call+0xdc/0x2d8
 Last Breaking-Event-Address:
   is_mem_section_removable+0xb4/0x190
 Kernel panic - not syncing: Fatal exception: panic_on_oops

The reason is that the memory block spans the zone boundary and we are
stumbling over an unitialized struct page.  Fix this by enforcing zone
range in is_mem_section_removable so that we never run away from a zone.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Michal Hocko <[email protected]>
Reported-by: Mikhail Zaslonko <[email protected]>
Debugged-by: Mikhail Zaslonko <[email protected]>
Tested-by: Gerald Schaefer <[email protected]>
Tested-by: Mikhail Gavrilov <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memory_hotplug.c

@@ -1233,7 +1233,8 @@ static bool is_pageblock_removable_nolock(struct page *page)
 bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
 {
 	struct page *page = pfn_to_page(start_pfn);
-	struct page *end_page = page + nr_pages;
+	unsigned long end_pfn = min(start_pfn + nr_pages, zone_end_pfn(page_zone(page)));
+	struct page *end_page = pfn_to_page(end_pfn);
 
 	/* Check the starting page of each pageblock within the range */
 	for (; page < end_page; page = next_active_pageblock(page)) {