On 5/18/2016 5:28 PM, Joonsoo Kim wrote:
Vlastiml, thanks for ccing me on original bug report.
On Wed, May 18, 2016 at 03:23:45PM -0700, Yang Shi wrote:
When enabling the below kernel configs:
CONFIG_DEFERRED_STRUCT_PAGE_INIT
CONFIG_DEBUG_PAGEALLOC
CONFIG_PAGE_EXTENSION
CONFIG_DEBUG_VM
kernel bootup may fail due to the following oops:
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0
PGD 0
Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
Modules linked in:
CPU: 11 PID: 106 Comm: pgdatinit1 Not tainted 4.6.0-rc5-next-20160427 #26
Hardware name: Intel Corporation S5520HC/S5520HC, BIOS S5500.86B.01.10.0025.030220091519 03/02/2009
task: ffff88017c080040 ti: ffff88017c084000 task.ti: ffff88017c084000
RIP: 0010:[<ffffffff8118d982>] [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0
RSP: 0000:ffff88017c087c48 EFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 0000000000000980 RSI: 0000000000000080 RDI: 0000000000660401
RBP: ffff88017c087cd0 R08: 0000000000000401 R09: 0000000000000009
R10: ffff88017c080040 R11: 000000000000000a R12: 0000000000000400
R13: ffffea0019810000 R14: ffffea0019810040 R15: ffff88066cfe6080
FS: 0000000000000000(0000) GS:ffff88066cd40000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000002406000 CR4: 00000000000006e0
Stack:
ffff88066cd5bbd8 ffff88066cfe6640 0000000000000000 0000000000000000
0000001f0000001f ffff88066cd5bbe8 ffffea0019810000 000000008118f53e
0000000000000009 0000000000000401 ffffffff0000000a 0000000000000001
Call Trace:
[<ffffffff8118f602>] free_hot_cold_page+0x192/0x1d0
[<ffffffff8118f69c>] __free_pages+0x5c/0x90
[<ffffffff8262a676>] __free_pages_boot_core+0x11a/0x14e
[<ffffffff8262a6fa>] deferred_free_range+0x50/0x62
[<ffffffff8262aa46>] deferred_init_memmap+0x220/0x3c3
[<ffffffff8262a826>] ? setup_per_cpu_pageset+0x35/0x35
[<ffffffff8108b1f8>] kthread+0xf8/0x110
[<ffffffff81c1b732>] ret_from_fork+0x22/0x40
[<ffffffff8108b100>] ? kthread_create_on_node+0x200/0x200
Code: 49 89 d4 48 c1 e0 06 49 01 c5 e9 de fe ff ff 4c 89 f7 44 89 4d b8 4c 89 45 c0 44 89 5d c8 48 89 4d d0 e8 62 c7 07 00 48 8b 4d d0 <48> 8b 00 44 8b 5d c8 4c 8b 45 c0 44 8b 4d b8 a8 02 0f 84 05 ff
RIP [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0
RSP <ffff88017c087c48>
CR2: 0000000000000000
The problem is lookup_page_ext() returns NULL then page_is_guard() tried to
access it in page freeing.
page_is_guard() depends on PAGE_EXT_DEBUG_GUARD bit of page extension flag, but
freeing page might reach here before the page_ext arrays are allocated when
feeding a range of pages to the allocator for the first time during bootup or
memory hotplug.
Patch itself looks find to me because I also found that this kind of
problem happens during memory hotplug. So, we need to fix more sites,
all callers of lookup_page_ext().
Yes, I agree. I will come up with a patch or a couple of patches to
check the return value of lookup_page_ext().
But, I'd like to know how your problem occurs during bootup.
debug_guardpage_enabled() is turned to 'enable' after page_ext is
initialized. Before that, page_is_guard() unconditionally returns
false so I think that the problem what you mentioned can't happen.
Could you check that when debug_guardpage_enabled() returns 'enable'
and init_section_page_ext() is called?
I think the problem is I have CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled,
which will defer some struct pages initialization to "pgdatinitX" kernel
thread in page_alloc_init_late(). But, page_ext_init() is called before it.
So, it leads debug_guardpage_enabled() return true, but page extension
is not allocated yet for the struct pages initialized by "pgdatinitX".
It sounds page_ext_init() should be called after page_alloc_init_late().
Or it should be just incompatible with CONFIG_DEFERRED_STRUCT_PAGE_INIT.
I will try to move the init call around.
Thanks,
Yang
And, above comment would be stale because it comes from when memcg uses
this struct page extension funtionality. Now, memcg doesn't use it and
there are some changes on this area so I'm not sure that is still true.
Thanks.
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