Re: [PATCH] mm: move page_ext_init after all struct pages are initialized

[Shi, Yang]

On 5/19/2016 3:30 PM, Andrew Morton wrote:
> On Thu, 19 May 2016 14:29:05 -0700 Yang Shi <yang.shi@xxxxxxxxxx> wrote:
>
> > When DEFERRED_STRUCT_PAGE_INIT is enabled, just a subset of memmap at boot
> > are initialized, then the rest are initialized in parallel by starting one-off
> > "pgdatinitX" kernel thread for each node X.
> >
> > If page_ext_init is called before it, some pages will not have valid extension,
> > so move page_ext_init() after it.
>
> <stdreply>When fixing a bug, please fully describe the end-user impact
> of that bug</>

The kernel ran into the below oops which is same with the oops reported 
in 
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_is_guard-return-false-when-page_ext-arrays-are-not-allocated-yet.patch.

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


I will add the oops info into the commit log in V2.

Thanks,
Yang

>