On Sun, Oct 6, 2013 at 10:08 PM, Toralf Förster <toralf.foers...@gmx.de> wrote:
> On 10/06/2013 08:38 PM, Geert Uytterhoeven wrote:
>> On Sun, Oct 6, 2013 at 4:17 PM, Toralf Förster <toralf.foers...@gmx.de>
>> wrote:
>>> The UML stopped here :
>>> ...
>>> if (unlikely(task_ratelimit == 0)) {
>>> period = max_pause;
>>> pause = max_pause;
>>> BUG_ON(pause < 0);
>>> goto pause;
>>> }
>>> BUG_ON(pages_dirtied < 0);
>>> BUG_ON(task_ratelimit < 0);
>>> period = HZ * pages_dirtied / task_ratelimit;
>>> BUG_ON(period < 0); <----------------------here
>>
>> So pages_dirtied becomes that big compared to task_ratelimit (both are
>> "unsigned long"), that period (which is "long", just like "pause") overflows
>> into a negative number.
>>
>> This is indeed much more likely to happen on 32-bit.
>>
>>> The back trace is :
>>
>>> #9 0x08411c64 in balance_dirty_pages (pages_dirtied=9, mapping=<optimized
>>> out>) at mm/page-writeback.c:1471
>>
>> But here pages_dirtied is only 9??
> Well, this points to an overflow or ? :
Negative indicates an overflow, but pages_dirtied doesn't.
> tfoerste@n22 ~/devel/linux $ nl -ba mm/page-writeback.c | grep -A 5 -B 5 1468
> 1463 BUG_ON(pause < 0);
> 1464 goto pause;
> 1465 }
> 1466 period = HZ * pages_dirtied / task_ratelimit;
> 1467 pause = period;
> 1468 BUG_ON(pause < 0 && pages_dirtied > 0 &&
> task_ratelimit > 0);
> 1469 if (current->dirty_paused_when)
> 1470 pause -= now - current->dirty_paused_when;
> 1471 /*
> 1472 * For less than 1s think time (ext3/4 may block the
> dirtier
> 1473 * for up to 800ms from time to time on 1-HDD; so
> does xfs,
>
>
> and the back trace is :
>
> #9 0x08411c6c in balance_dirty_pages (pages_dirtied=0, mapping=<optimized
> out>) at mm/page-writeback.c:1468
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
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@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
------------------------------------------------------------------------------
October Webinars: Code for Performance
Free Intel webinars can help you accelerate application performance.
Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from
the latest Intel processors and coprocessors. See abstracts and register >
http://pubads.g.doubleclick.net/gampad/clk?id=60134791&iu=/4140/ostg.clktrk
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
