4.20-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vitaly Kuznetsov vkuznets@redhat.com
commit da8ced360ca8ad72d8f41f5c8fcd5b0e63e1555f upstream.
Hyper-V memory hotplug protocol has 2M granularity and in Linux x86 we use 128M. To deal with it we implement partial section onlining by registering custom page onlining callback (hv_online_page()). Later, when more memory arrives we try to online the 'tail' (see hv_bring_pgs_online()).
It was found that in some cases this 'tail' onlining causes issues:
BUG: Bad page state in process kworker/0:2 pfn:109e3a page:ffffe08344278e80 count:0 mapcount:1 mapping:0000000000000000 index:0x0 flags: 0xfffff80000000() raw: 000fffff80000000 dead000000000100 dead000000000200 0000000000000000 raw: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 page dumped because: nonzero mapcount ... Workqueue: events hot_add_req [hv_balloon] Call Trace: dump_stack+0x5c/0x80 bad_page.cold.112+0x7f/0xb2 free_pcppages_bulk+0x4b8/0x690 free_unref_page+0x54/0x70 hv_page_online_one+0x5c/0x80 [hv_balloon] hot_add_req.cold.24+0x182/0x835 [hv_balloon] ...
Turns out that we now have deferred struct page initialization for memory hotplug so e.g. memory_block_action() in drivers/base/memory.c does pages_correctly_probed() check and in that check it avoids inspecting struct pages and checks sections instead. But in Hyper-V balloon driver we do PageReserved(pfn_to_page()) check and this is now wrong.
Switch to checking online_section_nr() instead.
Signed-off-by: Vitaly Kuznetsov vkuznets@redhat.com Cc: stable@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/hv/hv_balloon.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- a/drivers/hv/hv_balloon.c +++ b/drivers/hv/hv_balloon.c @@ -888,12 +888,14 @@ static unsigned long handle_pg_range(uns pfn_cnt -= pgs_ol; /* * Check if the corresponding memory block is already - * online by checking its last previously backed page. - * In case it is we need to bring rest (which was not - * backed previously) online too. + * online. It is possible to observe struct pages still + * being uninitialized here so check section instead. + * In case the section is online we need to bring the + * rest of pfns (which were not backed previously) + * online too. */ if (start_pfn > has->start_pfn && - !PageReserved(pfn_to_page(start_pfn - 1))) + online_section_nr(pfn_to_section_nr(start_pfn))) hv_bring_pgs_online(has, start_pfn, pgs_ol);
}