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Message-ID: <20131009214733.GB25608@quack.suse.cz>
Date: Wed, 9 Oct 2013 23:47:33 +0200
From: Jan Kara <jack@...e.cz>
To: Richard Weinberger <richard@....at>
Cc: Toralf Förster <toralf.foerster@....de>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
UML devel <user-mode-linux-devel@...ts.sourceforge.net>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
Jan Kara <jack@...e.cz>, hannes@...xchg.org,
darrick.wong@...cle.com, Michal Hocko <mhocko@...e.cz>,
Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [uml-devel] BUG: soft lockup for a user mode linux image
On Wed 09-10-13 20:43:50, Richard Weinberger wrote:
> CC'ing mm folks.
> Please see below.
Added Fenguang to CC since he is the author of this code.
> 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@....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.
Huh, this is really strange. pages_dirtied is passed into
balance_dirty_pages() from current->nr_dirtied. So I wonder how a value
over 10^9 can get there. After all that is over 4TB so I somewhat doubt the
task was ever able to dirty that much during its lifetime (but correct me
if I'm wrong here, with UML and memory backed disks it is not totally
impossible)... I went through the logic of handling ->nr_dirtied but
I didn't find any obvious problem there. Hum, maybe one thing - what
'task_ratelimit' values do you see in balance_dirty_pages? If that one was
huge, we could possibly accumulate huge current->nr_dirtied.
> 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.
>
>
> > 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 ?? ()
Honza
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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