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Subject[mmotm] BUG: Bad page state in process khugepaged ?

In environment
- Host: kernel-2.6.32xxx (RHEL6)
- Guest: mm-of-the-moment snapshot 2011-02-04-15-15

I saw this when I ran make -j8 under 200M limit of memcg with 4vcpu.
But it seems this doesn't directly related to memcg or virtualization.

Anyway, log is here. I'm sorry if this is a fixed one.
My .config is attached. and a brief note is below


==
Feb 9 14:39:54 rhel6-test kernel: [ 4209.076861] BUG: Bad page state in process khugepaged pfn:1e9800
Feb 9 14:39:54 rhel6-test kernel: [ 4209.077601] page:ffffea0006b14000 count:0 mapcount:0 mapping: (null) index:0x2800
Feb 9 14:39:54 rhel6-test kernel: [ 4209.078674] page flags: 0x40000000004000(head)
Feb 9 14:39:54 rhel6-test kernel: [ 4209.079294] pc:ffff880214a30000 pc->flags:2146246697418756 pc->mem_cgroup:ffffc9000177a000
Feb 9 14:39:54 rhel6-test kernel: [ 4209.082177] (/A)
Feb 9 14:39:54 rhel6-test kernel: [ 4209.082500] Pid: 31, comm: khugepaged Not tainted 2.6.38-rc3-mm1 #1
Feb 9 14:39:54 rhel6-test kernel: [ 4209.083412] Call Trace:
Feb 9 14:39:54 rhel6-test kernel: [ 4209.083678] [<ffffffff810f4454>] ? bad_page+0xe4/0x140
Feb 9 14:39:54 rhel6-test kernel: [ 4209.084240] [<ffffffff810f53e6>] ? free_pages_prepare+0xd6/0x120
Feb 9 14:39:54 rhel6-test kernel: [ 4209.084837] [<ffffffff8155621d>] ? rwsem_down_failed_common+0xbd/0x150
Feb 9 14:39:54 rhel6-test kernel: [ 4209.085509] [<ffffffff810f5462>] ? __free_pages_ok+0x32/0xe0
Feb 9 14:39:54 rhel6-test kernel: [ 4209.086110] [<ffffffff810f552b>] ? free_compound_page+0x1b/0x20
Feb 9 14:39:54 rhel6-test kernel: [ 4209.086699] [<ffffffff810fad6c>] ? __put_compound_page+0x1c/0x30
Feb 9 14:39:54 rhel6-test kernel: [ 4209.087333] [<ffffffff810fae1d>] ? put_compound_page+0x4d/0x200
Feb 9 14:39:54 rhel6-test kernel: [ 4209.087935] [<ffffffff810fb015>] ? put_page+0x45/0x50
Feb 9 14:39:54 rhel6-test kernel: [ 4209.097361] [<ffffffff8113f779>] ? khugepaged+0x9e9/0x1430
Feb 9 14:39:54 rhel6-test kernel: [ 4209.098364] [<ffffffff8107c870>] ? autoremove_wake_function+0x0/0x40
Feb 9 14:39:54 rhel6-test kernel: [ 4209.099121] [<ffffffff8113ed90>] ? khugepaged+0x0/0x1430
Feb 9 14:39:54 rhel6-test kernel: [ 4209.099780] [<ffffffff8107c236>] ? kthread+0x96/0xa0
Feb 9 14:39:54 rhel6-test kernel: [ 4209.100452] [<ffffffff8100dda4>] ? kernel_thread_helper+0x4/0x10
Feb 9 14:39:54 rhel6-test kernel: [ 4209.101214] [<ffffffff8107c1a0>] ? kthread+0x0/0xa0
Feb 9 14:39:54 rhel6-test kernel: [ 4209.101842] [<ffffffff8100dda0>] ? kernel_thread_helper+0x0/0x10
Feb 9 14:39:54 rhel6-test kernel: [ 4209.102575] ------------[ cut here ]------------
Feb 9 14:39:54 rhel6-test kernel: [ 4209.103190] kernel BUG at include/linux/mm.h:420!
Feb 9 14:39:54 rhel6-test kernel: [ 4209.103803] invalid opcode: 0000 [#1] SMP
Feb 9 14:39:54 rhel6-test kernel: [ 4209.104309] last sysfs file: /sys/devices/system/cpu/online
Feb 9 14:39:54 rhel6-test kernel: [ 4209.104991] CPU 0
Feb 9 14:39:54 rhel6-test kernel: [ 4209.105244] Modules linked in: autofs4 sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables ipv6 virtio_balloon virtio_net virtio_blk virtio_pci virtio_ring virtio [last unloaded: scsi_wait_scan]
Feb 9 14:39:54 rhel6-test kernel: [ 4209.108135]
Feb 9 14:39:54 rhel6-test kernel: [ 4209.108303] Pid: 31, comm: khugepaged Not tainted 2.6.38-rc3-mm1 #1 /KVM
Feb 9 14:39:54 rhel6-test kernel: [ 4209.109098] RIP: 0010:[<ffffffff810f4486>] [<ffffffff810f4486>] bad_page+0x116/0x140
Feb 9 14:39:54 rhel6-test kernel: [ 4209.110086] RSP: 0000:ffff880211f99ca0 EFLAGS: 00010202
Feb 9 14:39:54 rhel6-test kernel: [ 4209.110747] RAX: 00000000ffffffff RBX: ffffea0006b14000 RCX: 0000000000000712
Feb 9 14:39:54 rhel6-test kernel: [ 4209.111601] RDX: 00000000ffffffff RSI: 0000000000000001 RDI: ffff880211f99f58
Feb 9 14:39:54 rhel6-test kernel: [ 4209.112491] RBP: ffff880211f99cb0 R08: ffffffff81b41b80 R09: 0000000000000200
Feb 9 14:39:54 rhel6-test kernel: [ 4209.119933] R10: 0000000000000006 R11: 0000000000000001 R12: 0000000000000200
Feb 9 14:39:54 rhel6-test kernel: [ 4209.120764] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Feb 9 14:39:54 rhel6-test kernel: [ 4209.121623] FS: 0000000000000000(0000) GS:ffff8800dfc00000(0000) knlGS:0000000000000000
Feb 9 14:39:54 rhel6-test kernel: [ 4209.122523] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
Feb 9 14:39:54 rhel6-test kernel: [ 4209.123195] CR2: 0000000000b9dd90 CR3: 00000001ffeaf000 CR4: 00000000000006f0
Feb 9 14:39:54 rhel6-test kernel: [ 4209.123951] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Feb 9 14:39:54 rhel6-test kernel: [ 4209.124765] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Feb 9 14:39:54 rhel6-test kernel: [ 4209.125610] Process khugepaged (pid: 31, threadinfo ffff880211f98000, task ffff880211f34590)
Feb 9 14:39:54 rhel6-test kernel: [ 4209.126529] Stack:
Feb 9 14:39:54 rhel6-test kernel: [ 4209.126793] ffff880211f99cb0 ffffea0006b14000 ffff880211f99d00 ffffffff810f53e6
Feb 9 14:39:54 rhel6-test kernel: [ 4209.127725] ffff880211f99d20 ffffffff8155621d dead000000100100 ffffea0006b14000
Feb 9 14:39:54 rhel6-test kernel: [ 4209.130864] 0000000000000009 0000000000000019 0000000000000000 0000000000000447
Feb 9 14:39:54 rhel6-test kernel: [ 4209.131766] Call Trace:
Feb 9 14:39:54 rhel6-test kernel: [ 4209.132236] [<ffffffff810f53e6>] free_pages_prepare+0xd6/0x120
Feb 9 14:39:54 rhel6-test kernel: [ 4209.132891] [<ffffffff8155621d>] ? rwsem_down_failed_common+0xbd/0x150
Feb 9 14:39:54 rhel6-test kernel: [ 4209.133864] [<ffffffff810f5462>] __free_pages_ok+0x32/0xe0
Feb 9 14:39:54 rhel6-test kernel: [ 4209.134518] [<ffffffff810f552b>] free_compound_page+0x1b/0x20
Feb 9 14:39:54 rhel6-test kernel: [ 4209.135244] [<ffffffff810fad6c>] __put_compound_page+0x1c/0x30
Feb 9 14:39:54 rhel6-test kernel: [ 4209.135934] [<ffffffff810fae1d>] put_compound_page+0x4d/0x200
Feb 9 14:39:54 rhel6-test kernel: [ 4209.136659] [<ffffffff810fb015>] put_page+0x45/0x50
Feb 9 14:39:54 rhel6-test kernel: [ 4209.137232] [<ffffffff8113f779>] khugepaged+0x9e9/0x1430
Feb 9 14:39:54 rhel6-test kernel: [ 4209.137801] [<ffffffff8107c870>] ? autoremove_wake_function+0x0/0x40
Feb 9 14:39:54 rhel6-test kernel: [ 4209.138527] [<ffffffff8113ed90>] ? khugepaged+0x0/0x1430
Feb 9 14:39:54 rhel6-test kernel: [ 4209.139166] [<ffffffff8107c236>] kthread+0x96/0xa0
Feb 9 14:39:54 rhel6-test kernel: [ 4209.139707] [<ffffffff8100dda4>] kernel_thread_helper+0x4/0x10
Feb 9 14:39:54 rhel6-test kernel: [ 4209.140334] [<ffffffff8107c1a0>] ? kthread+0x0/0xa0
Feb 9 14:39:54 rhel6-test kernel: [ 4209.140901] [<ffffffff8100dda0>] ? kernel_thread_helper+0x0/0x10
Feb 9 14:39:54 rhel6-test kernel: [ 4209.141582] Code: 35 f0 19 c1 00 48 85 f6 75 25 48 c7 05 e8 19 c1 00 01 00 00 00 48 8b 05 49 54 a5 00 48 05 60 ea 00 00 48 89 05 dc 19 c1 00 eb 83 <0f> 0b eb fe 48 c7 c7 30 5a 7a 81 31 c0 e8 e0 f0 45 00 48 c7 05
==

2nd log, "kernel BUG at include/linux/mm.h:420!" is This one.
==
static inline void __ClearPageBuddy(struct page *page)
{
VM_BUG_ON(!PageBuddy(page));
atomic_set(&page->_mapcount, -1);
}
==
But this is just a tail of bad_page().
==
static void bad_page(struct page *page)
{
static unsigned long resume;
static unsigned long nr_shown;
static unsigned long nr_unshown;
...
dump_stack();
out:
/* Leave bad fields for debug, except PageBuddy could make trouble */
__ClearPageBuddy(page);
add_taint(TAINT_BAD_PAGE);
}
==
So, what important is bad_page().
BAD page says
==
BUG: Bad page state in process khugepaged pfn:1e9800
page:ffffea0006b14000 count:0 mapcount:0 mapping: (null) index:0x2800
page flags: 0x40000000004000(head)
pc:ffff880214a30000 pc->flags:2146246697418756 pc->mem_cgroup:ffffc9000177a000
==
Maybe page_mapcount(page) was > 0. and ->mapping was NULL.
BTW, I think pc->flags should be printed in hex...Nishimura-san, how do you think ?


In hex, pc->flags was 7A00000000004 and this means PCG_USED bit is set.
This implies page_remove_rmap() may not be called but ->mapping is NULL. Hmm?
(7A is encoding of section number.)
make -j 8 under 200M limit is highly busy with swap.

Thanks,
-Kame
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