From: Michal Hocko <mhocko@xxxxxxxx>
Subject: 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
2830bf6f05fb ("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/20181105150401.97287-2-zaslonko@xxxxxxxxxxxxx
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1666948
[3] http://lkml.kernel.org/r/20190125163938.GA20411@xxxxxxxxxxxxxx
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:
([<000000000038596c>] is_mem_section_removable+0xb4/0x190)
[<00000000008f12fa>] show_mem_removable+0x9a/0xd8
[<00000000008cf9c4>] dev_attr_show+0x34/0x70
[<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148
[<00000000003e4194>] seq_read+0x204/0x480
[<00000000003b53ea>] __vfs_read+0x32/0x178
[<00000000003b55b2>] vfs_read+0x82/0x138
[<00000000003b5be2>] ksys_read+0x5a/0xb0
[<0000000000b86ba0>] system_call+0xdc/0x2d8
Last Breaking-Event-Address:
[<000000000038596c>] 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/20190128144506.15603-2-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reported-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>
Debugged-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>
Tested-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory_hotplug.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/memory_hotplug.c~mm-memory_hotplug-is_mem_section_removable-do-not-pass-the-end-of-a-zone
+++ a/mm/memory_hotplug.c
@@ -1233,7 +1233,8 @@ static bool is_pageblock_removable_noloc
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)) {
_
