On 04.01.19 15:19, Vitaly Kuznetsov wrote: > 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@xxxxxxxxxx> > --- > drivers/hv/hv_balloon.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c > index 5301fef16c31..7c6349a50ef1 100644 > --- a/drivers/hv/hv_balloon.c > +++ b/drivers/hv/hv_balloon.c > @@ -888,12 +888,14 @@ static unsigned long handle_pg_range(unsigned long pg_start, > 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); > > } > I wonder if you should use pfn_to_online_page() and check for PageOffline(). (I guess online_section_nr() should also do the trick) -- Thanks, David / dhildenb _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
