From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: devel@linuxdriverproject.org
Cc: Sasha Levin <sashal@kernel.org>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
linux-kernel@vger.kernel.org, Dexuan Cui <decui@microsoft.com>
Subject: [PATCH] hv_balloon: avoid touching uninitialized struct page during tail onlining
Date: Fri, 4 Jan 2019 15:19:42 +0100 [thread overview]
Message-ID: <20190104141942.19126-1-vkuznets@redhat.com> (raw)
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>
---
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);
}
--
2.20.1
next reply other threads:[~2019-01-04 14:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-04 14:19 Vitaly Kuznetsov [this message]
2019-01-07 10:21 ` [PATCH] hv_balloon: avoid touching uninitialized struct page during tail onlining David Hildenbrand
2019-01-07 13:44 ` Vitaly Kuznetsov
2019-01-07 17:56 ` Sasha Levin
2019-01-07 18:38 ` Vitaly Kuznetsov
2019-01-08 6:41 ` Greg KH
2019-01-08 9:47 ` Dan Carpenter
2019-01-08 14:34 ` Vitaly Kuznetsov
2019-01-08 21:23 ` Sasha Levin
2019-01-08 9:15 ` David Hildenbrand
2019-01-08 9:42 ` Vitaly Kuznetsov
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