Re: page allocator regression on nommu

[Pekka Enberg]

Hi Paul,

On Mon, Aug 31, 2009 at 10:48 AM, Paul Mundt<lethal@xxxxxxxxxxxx> wrote:
> It seems we've managed to trigger a fairly interesting conflict between
> the anti-fragmentation disabling code and the nommu region rbtree. I've
> bisected it down to:
>
> commit 49255c619fbd482d704289b5eb2795f8e3b7ff2e
> Author: Mel Gorman <mel@xxxxxxxxx>
> Date:   Tue Jun 16 15:31:58 2009 -0700
>
>    page allocator: move check for disabled anti-fragmentation out of fastpath
>
>    On low-memory systems, anti-fragmentation gets disabled as there is
>    nothing it can do and it would just incur overhead shuffling pages between
>    lists constantly.  Currently the check is made in the free page fast path
>    for every page.  This patch moves it to a slow path.  On machines with low
>    memory, there will be small amount of additional overhead as pages get
>    shuffled between lists but it should quickly settle.
>
> which causes death on unpacking initramfs on my nommu board. With this
> reverted, everything works as expected. Note that this blows up with all of
> SLOB/SLUB/SLAB.
>
> I'll continue debugging it, and can post my .config if it will be helpful, but
> hopefully you have some suggestions on what to try :-)
>
> ---
>
> modprobe: page allocation failure. order:7, mode:0xd0

OK, so we have order 7 page allocation here...

> Stack: (0x0c909d2c to 0x0c90a000)
> 9d20:                            0c0387d2 00000000 00000000 0c107fcc 00000000
> 9d40: 00000000 0c107fcc 0c2f8960 00000000 00000010 00000000 00000000 000200d0
> 9d60: 00000000 0c041614 0c9f8cf4 00000000 0c9f8d1c 00000000 00000004 00000000
> 9d80: 00000007 0c01a582 0c2f8cd0 00000000 00000000 00049000 00000049 00048fff
> 9da0: 00049fff 00049000 00000007 0c06633a 00000001 0c909f30 0003e950 0c0bad00
> 9dc0: 0000984a 0c2f8ea0 ffffe000 00000002 00000000 0c065314 0c2f8ea0 0c077f60
> 9de0: 00049000 0000673c 00000050 000369a0 000019cf 00000004 00004e20 0003e950
> 9e00: 000481aa 00000001 00004eaa 000049a0 00007fb0 000369a0 00000000 00000000
> 9e20: 0c909e50 00000000 00000000 0c066790 00000000 0c909f30 00000000 00000000
> 9e40: 0c2f8ea0 0c909f30 0c909e50 00004eaa 00000000 00000000 00000000 00000000
> 9e60: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 9e80: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 9ea0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 9ec0: 0c0482ee 00000000 fffffff8 0c2f8ea0 0c104ff8 0c04884e 0c0feb64 00000001
> 9ee0: 0c048570 ffffe000 0c2f8ea0 00000000 00000000 0c813eb8 0c909f30 0c002e68
> 9f00: 00000000 00000000 00000000 0c0feb64 0c813eb8 0c909f30 0c960000 0c007972
> 9f20: ffffff0f 00000071 00000100 0c002e38 0000000b ffffff0f 00000001 0000000b
> 9f40: 0c0fea64 0c813eb8 0c0feb64 0c2f898c 00000000 ffffe000 0c9f8990 00000000
> 9f60: 00000000 00000000 00000000 0c909f8c 0c0050ca 0c01e874 40000001 00000000
> 9f80: 00000000 4795ce40 0000004c 0c002cca 00000000 00000000 00000000 00000000
> 9fa0: 00000000 00000000 00000000 00000000 00000000 0c9f8990 0c01e7a4 00000000
> 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 9fe0: 0c909f9c 0c002cc4 00000000 40000000 00000000 00000000 00000000 00000000
>
> Call trace:
>  [<0c041614>] do_mmap_pgoff+0x638/0xa68
>  [<0c01a582>] flush_itimer_signals+0x36/0x60
>  [<0c06633a>] load_flat_file+0x32a/0x738
>  [<0c0bad00>] down_write+0x0/0xc
>  [<0c065314>] load_elf_fdpic_binary+0x44/0xa8c
>  [<0c077f60>] memset+0x0/0x60
>  [<0c066790>] load_flat_binary+0x48/0x2fc
>  [<0c0482ee>] search_binary_handler+0x4a/0x1fc
>  [<0c04884e>] do_execve+0x156/0x2bc
>  [<0c048570>] copy_strings+0x0/0x150
>  [<0c002e68>] sys_execve+0x30/0x5c
>  [<0c007972>] syscall_call+0xc/0x10
>  [<0c002e38>] sys_execve+0x0/0x5c
>  [<0c0050ca>] kernel_execve+0x6/0xc
>  [<0c01e874>] ____call_usermodehelper+0xd0/0xfc
>  [<0c002cca>] kernel_thread_helper+0x6/0x10
>  [<0c01e7a4>] ____call_usermodehelper+0x0/0xfc
>  [<0c002cc4>] kernel_thread_helper+0x0/0x10
>
> Mem-Info:
> Normal per-cpu:
> CPU    0: hi:    0, btch:   1 usd:   0
> Active_anon:0 active_file:0 inactive_anon:0
>  inactive_file:0 unevictable:323 dirty:0 writeback:0 unstable:0
>  free:2967 slab:0 mapped:0 pagetables:0 bounce:0
> Normal free:11868kB min:0kB low:0kB high:0kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:1292kB present:16256kB pages_scanned:0 all_unreclaimable? no
> lowmem_reserve[]: 0 0
> Normal: 267*4kB 268*8kB 251*16kB 145*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB 0*8192kB 0*16384kB 0*32768kB = 11868kB

...but we seem to be all out of order > 3 pages. I'm not sure why
commit 49255c619fbd482d704289b5eb2795f8e3b7ff2e changes any of this,
though.

> 323 total pagecache pages
> ------------[ cut here ]------------
> kernel BUG at mm/nommu.c:598!
> Kernel BUG: 003e [#1]
> Modules linked in:
>
> Pid : 51, Comm:                 modprobe
> CPU : 0                 Not tainted  (2.6.31-rc7 #2835)
>
> PC is at __put_nommu_region+0xe/0xb0
> PR is at do_mmap_pgoff+0x8dc/0xa68

This looks to be a bug in nommu do_mmap_pgoff() error handling. I
guess we shouldn't call __put_nommu_region() if add_nommu_region()
hasn't been called?

> PC  : 0c040e7a SP  : 0c909d7c SR  : 40000001
> R0  : 0000001d R1  : 00000000 R2  : 00000000 R3  : 0000000d
> R4  : 0c9f8cf4 R5  : 000017de R6  : ffffffff R7  : 00000035
> R8  : 0c9f8cf4 R9  : 00000000 R10 : 00000000 R11 : fffffff4
> R12 : 0c9f8d1c R13 : 00000000 R14 : 0c9f8cf4
> MACH: 0000017e MACL: baf11680 GBR : 00000000 PR  : 0c0418b8
>
> Call trace:
>  [<0c0418b8>] do_mmap_pgoff+0x8dc/0xa68
>  [<0c01a582>] flush_itimer_signals+0x36/0x60
>  [<0c06633a>] load_flat_file+0x32a/0x738
>  [<0c0bad00>] down_write+0x0/0xc
>  [<0c065314>] load_elf_fdpic_binary+0x44/0xa8c
>  [<0c077f60>] memset+0x0/0x60
>  [<0c066790>] load_flat_binary+0x48/0x2fc
>  [<0c0482ee>] search_binary_handler+0x4a/0x1fc
>  [<0c04884e>] do_execve+0x156/0x2bc
>  [<0c048570>] copy_strings+0x0/0x150
>  [<0c002e68>] sys_execve+0x30/0x5c
>  [<0c007972>] syscall_call+0xc/0x10
>  [<0c002e38>] sys_execve+0x0/0x5c
>  [<0c0050ca>] kernel_execve+0x6/0xc
>  [<0c01e874>] ____call_usermodehelper+0xd0/0xfc
>  [<0c002cca>] kernel_thread_helper+0x6/0x10
>  [<0c01e7a4>] ____call_usermodehelper+0x0/0xfc
>  [<0c002cc4>] kernel_thread_helper+0x0/0x10
>
> Code:
>  0c040e74:  tst       r1, r1
>  0c040e76:  bf.s      0c040e7c
>  0c040e78:  mov       r4, r8
> ->0c040e7a:  trapa     #62
>  0c040e7c:  stc       sr, r1
>  0c040e7e:  mov       r1, r0
>  0c040e80:  or        #-16, r0
>  0c040e82:  ldc       r0, sr
>  0c040e84:  mov       r1, r0
>
> Process: modprobe (pid: 51, stack limit = 0c908001)
> Stack: (0x0c909d7c to 0x0c90a000)
> 9d60:                                                                0c0418b8
> 9d80: 00000007 0c01a582 0c2f8cd0 00000000 00000000 00049000 00000049 00048fff
> 9da0: 00049fff 00049000 00000007 0c06633a 00000001 0c909f30 0003e950 0c0bad00
> 9dc0: 0000984a 0c2f8ea0 ffffe000 00000002 00000000 0c065314 0c2f8ea0 0c077f60
> 9de0: 00049000 0000673c 00000050 000369a0 000019cf 00000004 00004e20 0003e950
> 9e00: 000481aa 00000001 00004eaa 000049a0 00007fb0 000369a0 00000000 00000000
> 9e20: 0c909e50 00000000 00000000 0c066790 00000000 0c909f30 00000000 00000000
> 9e40: 0c2f8ea0 0c909f30 0c909e50 00004eaa 00000000 00000000 00000000 00000000
> 9e60: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 9e80: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 9ea0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 9ec0: 0c0482ee 00000000 fffffff8 0c2f8ea0 0c104ff8 0c04884e 0c0feb64 00000001
> 9ee0: 0c048570 ffffe000 0c2f8ea0 00000000 00000000 0c813eb8 0c909f30 0c002e68
> 9f00: 00000000 00000000 00000000 0c0feb64 0c813eb8 0c909f30 0c960000 0c007972
> 9f20: ffffff0f 00000071 00000100 0c002e38 0000000b ffffff0f 00000001 0000000b
> 9f40: 0c0fea64 0c813eb8 0c0feb64 0c2f898c 00000000 ffffe000 0c9f8990 00000000
> 9f60: 00000000 00000000 00000000 0c909f8c 0c0050ca 0c01e874 40000001 00000000
> 9f80: 00000000 4795ce40 0000004c 0c002cca 00000000 00000000 00000000 00000000
> 9fa0: 00000000 00000000 00000000 00000000 00000000 0c9f8990 0c01e7a4 00000000
> 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 9fe0: 0c909f9c 0c002cc4 00000000 40000000 00000000 00000000 00000000 00000000
> ---[ end trace 139ce121c98e96c9 ]---
>
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