Re: [uml-devel] BUG: soft lockup for a user mode linux image

[Richard Weinberger <richard@nod.at>]

CC'ing mm folks.
Please see below.

Am 09.10.2013 19:26, schrieb Toralf Förster:
> On 10/08/2013 10:07 PM, Geert Uytterhoeven wrote:
>> On Sun, Oct 6, 2013 at 11:01 PM, Toralf Förster <toralf.foerster@gmx.de> wrote:
>>>> Hmm, now pages_dirtied is zero, according to the backtrace, but the BUG_ON()
>>>> asserts its strict positive?!?
>>>>
>>>> Can you please try the following instead of the BUG_ON():
>>>>
>>>> if (pause < 0) {
>>>>         printk("pages_dirtied = %lu\n", pages_dirtied);
>>>>         printk("task_ratelimit = %lu\n", task_ratelimit);
>>>>         printk("pause = %ld\n", pause);
>>>> }
>>>>
>>>> Gr{oetje,eeting}s,
>>>>
>>>>                         Geert
>>> I tried it in different ways already - I'm completely unsuccessful in getting any printk output.
>>> As soon as the issue happens I do have a
>>>
>>> BUG: soft lockup - CPU#0 stuck for 22s! [trinity-child0:1521]
>>>
>>> at stderr of the UML and then no further input is accepted. With uml_mconsole I'm however able
>>> to run very basic commands like a crash dump, sysrq ond so on.
>>
>> You may get an idea of the magnitude of pages_dirtied by using a chain of
>> BUG_ON()s, like:
>>
>> BUG_ON(pages_dirtied > 2000000000);
>> BUG_ON(pages_dirtied > 1000000000);
>> BUG_ON(pages_dirtied > 100000000);
>> BUG_ON(pages_dirtied > 10000000);
>> BUG_ON(pages_dirtied > 1000000);
>>
>> Probably 1 million is already too much for normal operation?
>>
> period = HZ * pages_dirtied / task_ratelimit;
> 		BUG_ON(pages_dirtied > 2000000000);
> 		BUG_ON(pages_dirtied > 1000000000);      <-------------- this is line 1467

Summary for mm people:

Toralf runs trinty on UML/i386.
After some time pages_dirtied becomes very large.
More than 1000000000 pages in this case.

Thus, period = HZ * pages_dirtied / task_ratelimit overflows
and period/pause becomes extremely large.

It looks like io_schedule_timeout() get's called with a very large timeout.
I don't know why "if (unlikely(pause > max_pause)) {" does not help.

Any ideas?

Thanks,
//richard

> the back trace is :
> 
> tfoerste@n22 ~/devel/linux $ gdb --core=/mnt/ramdisk/core /home/tfoerste/devel/linux/linux -batch -ex bt
> [New LWP 6911]
> Core was generated by `/home/tfoerste/devel/linux/linux earlyprintk ubda=/home/tfoerste/virtual/uml/tr'.
> Program terminated with signal 6, Aborted.
> #0  0xb77a7424 in __kernel_vsyscall ()
> #0  0xb77a7424 in __kernel_vsyscall ()
> #1  0x083bdf35 in kill ()
> #2  0x0807296d in uml_abort () at arch/um/os-Linux/util.c:93
> #3  0x08072ca5 in os_dump_core () at arch/um/os-Linux/util.c:148
> #4  0x080623c4 in panic_exit (self=0x85c1558 <panic_exit_notifier>, unused1=0, unused2=0x85f76e0 <buf.16221>) at arch/um/kernel/um_arch.c:240
> #5  0x0809ba86 in notifier_call_chain (nl=0x0, val=0, v=0x85f76e0 <buf.16221>, nr_to_call=-2, nr_calls=0x0) at kernel/notifier.c:93
> #6  0x0809bba1 in __atomic_notifier_call_chain (nh=0x85f76c4 <panic_notifier_list>, val=0, v=0x85f76e0 <buf.16221>, nr_to_call=0, nr_calls=0x0) at kernel/notifier.c:182
> #7  0x0809bbdf in atomic_notifier_call_chain (nh=0x0, val=0, v=0x0) at kernel/notifier.c:191
> #8  0x0841b5bc in panic (fmt=0x0) at kernel/panic.c:130
> #9  0x0841c470 in balance_dirty_pages (pages_dirtied=23, mapping=<optimized out>) at mm/page-writeback.c:1467
> #10 0x080d3595 in balance_dirty_pages_ratelimited (mapping=0x6) at mm/page-writeback.c:1661
> #11 0x080e4a3f in __do_fault (mm=0x45ba3600, vma=0x48777b90, address=1084678144, pmd=0x0, pgoff=0, flags=0, orig_pte=<incomplete type>) at mm/memory.c:3452
> #12 0x080e6e0f in do_linear_fault (orig_pte=..., flags=<optimized out>, pmd=<optimized out>, address=<optimized out>, vma=<optimized out>, mm=<optimized out>, page_table=<optimized out>) at mm/memory.c:3486
> #13 handle_pte_fault (flags=<optimized out>, pmd=<optimized out>, pte=<optimized out>, address=<optimized out>, vma=<optimized out>, mm=<optimized out>) at mm/memory.c:3710
> #14 __handle_mm_fault (flags=<optimized out>, address=<optimized out>, vma=<optimized out>, mm=<optimized out>) at mm/memory.c:3845
> #15 handle_mm_fault (mm=0x45ba3600, vma=0x487034c8, address=1084678144, flags=1) at mm/memory.c:3868
> #16 0x080e7817 in __get_user_pages (tsk=0x48705800, mm=0x45ba3600, start=1084678144, nr_pages=1025, gup_flags=519, pages=0x48558000, vmas=0x0, nonblocking=0x0) at mm/memory.c:1822
> #17 0x080e7ae3 in get_user_pages (tsk=0x0, mm=0x0, start=0, nr_pages=0, write=1, force=0, pages=0x48777b90, vmas=0x6) at mm/memory.c:2019
> #18 0x08143dc6 in aio_setup_ring (ctx=<optimized out>) at fs/aio.c:340
> #19 ioctx_alloc (nr_events=<optimized out>) at fs/aio.c:605
> #20 SYSC_io_setup (ctxp=<optimized out>, nr_events=<optimized out>) at fs/aio.c:1122
> #21 SyS_io_setup (nr_events=65535, ctxp=135081984) at fs/aio.c:1105
> #22 0x08062984 in handle_syscall (r=0x487059d4) at arch/um/kernel/skas/syscall.c:35
> #23 0x08074fb5 in handle_trap (local_using_sysemu=<optimized out>, regs=<optimized out>, pid=<optimized out>) at arch/um/os-Linux/skas/process.c:198
> #24 userspace (regs=0x487059d4) at arch/um/os-Linux/skas/process.c:431
> #25 0x0805f750 in fork_handler () at arch/um/kernel/process.c:160
> #26 0x00000000 in ?? ()
> 
> 
> 
>> Gr{oetje,eeting}s,
>>
>>                         Geert
>>
>> --
>> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>>
>> In personal conversations with technical people, I call myself a hacker. But
>> when I'm talking to journalists I just say "programmer" or something like that.
>>                                 -- Linus Torvalds
>>
> 
>