On Thu, Apr 18, 2013 at 09:13:03AM +0200, Heiko Carstens wrote:
> Ok, thanks for verifying! I'll look into it; hopefully I can reproduce it
> here as well.
That seems to be a common code bug. I can easily trigger the VM_BUG_ON()
below (when I force the system to swap):
[ 48.347963] ------------[ cut here ]------------
[ 48.347972] kernel BUG at mm/memcontrol.c:3994!
[ 48.348012] illegal operation: 0001 [#1] SMP
[ 48.348015] Modules linked in:
[ 48.348017] CPU: 1 Not tainted 3.9.0-rc8+ #38
[ 48.348020] Process mmap2 (pid: 635, task: 0000000029476100, ksp:
000000002e91b938)
[ 48.348022] Krnl PSW : 0704f00180000000 000000000026552c
(__mem_cgroup_uncharge_common+0x2c4/0x33c)
[ 48.348032] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:3 PM:0
EA:3
Krnl GPRS: 0000000000000008 0000000000000009 000003d1002a9200
0000000000000000
[ 48.348039] 0000000000000000 00000000006812d8 000003ffdf339000
00000000321a6f98
[ 48.348043] 000003fffce11000 0000000000000000 0000000000000001
000003d1002a9200
[ 48.348046] 0000000000000001 0000000000681b88 000000002e91bc18
000000002e91bbd0
[ 48.348057] Krnl Code: 000000000026551e: c0e5fffaa2a1 brasl
%r14,1b9a60
0000000000265524: a7f4ff7d brc
15,26541e
#0000000000265528: a7f40001 brc
15,26552a
>000000000026552c: e3c0b8200124 stg
%r12,6176(%r11)
0000000000265532: a7f4ff57 brc
15,2653e0
0000000000265536: e310b8280104 lg
%r1,6184(%r11)
000000000026553c: a71b0001 aghi %r1,1
0000000000265540: e310b8280124 stg
%r1,6184(%r11)
[ 48.348099] Call Trace:
[ 48.348100] ([<000003d1002a91c0>] 0x3d1002a91c0)
[ 48.348102] [<00000000002404aa>] page_remove_rmap+0xf2/0x16c
[ 48.348106] [<0000000000232dc8>] unmap_single_vma+0x494/0x7d8
[ 48.348107] [<0000000000233ac0>] unmap_vmas+0x50/0x74
[ 48.348109] [<00000000002396ec>] unmap_region+0x9c/0x110
[ 48.348110] [<000000000023bd18>] do_munmap+0x284/0x470
[ 48.348111] [<000000000023bf56>] vm_munmap+0x52/0x70
[ 48.348113] [<000000000023cf32>] SyS_munmap+0x3a/0x4c
[ 48.348114] [<0000000000665e14>] sysc_noemu+0x22/0x28
[ 48.348118] [<000003fffcf187b2>] 0x3fffcf187b2
[ 48.348119] Last Breaking-Event-Address:
[ 48.348120] [<0000000000265528>] __mem_cgroup_uncharge_common+0x2c0/0x33c
Looking at the code, the code flow is:
page_remove_rmap() -> mem_cgroup_uncharge_page() ->
__mem_cgroup_uncharge_common()
Note that in mem_cgroup_uncharge_page() the page in question passed the check:
[...]
if (PageSwapCache(page))
return;
[...]
and just a couple of instructions later the VM_BUG_ON() within
__mem_cgroup_uncharge_common() triggers:
[...]
if (mem_cgroup_disabled())
return NULL;
VM_BUG_ON(PageSwapCache(page));
[...]
Which means that another cpu changed the pageflags concurrently. In fact,
looking at the dump a different cpu is indeed busy with running kswapd.
So.. this seems to be somewhat broken. Anyone familiar with memcontrol?
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