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SubjectRe: [2.6.36-rc1] unmount livelock due to racing with bdi-flusher threads
ping?

On Sat, Aug 21, 2010 at 06:41:26PM +1000, Dave Chinner wrote:
> Folks,
>
> I just had an umount take a very long time burning a CPU the entire
> time. It wasn't the unmount thread, either, it was the the bdi
> flusher thread for the the filesystem being unmounted. It was
> spinning with this perf top trace:
>
> 553144.00 76.9% writeback_inodes_wb [kernel.kallsyms]
> 106434.00 14.8% __ticket_spin_lock [kernel.kallsyms]
> 25646.00 3.6% __ticket_spin_unlock [kernel.kallsyms]
> 10512.00 1.5% _raw_spin_lock [kernel.kallsyms]
> 9606.00 1.3% put_super [kernel.kallsyms]
> 7920.00 1.1% __put_super [kernel.kallsyms]
> 5592.00 0.8% down_read_trylock [kernel.kallsyms]
> 46.00 0.0% kfree [kernel.kallsyms]
> 22.00 0.0% __do_softirq [kernel.kallsyms]
> 19.00 0.0% wb_writeback [kernel.kallsyms]
> 16.00 0.0% wb_do_writeback [kernel.kallsyms]
> 8.00 0.0% queue_io [kernel.kallsyms]
> 6.00 0.0% run_timer_softirq [kernel.kallsyms]
> 6.00 0.0% local_bh_enable_ip [kernel.kallsyms]
>
> This went on for ~7m25s (according to the pmchart trace I had on
> screen) before something broke the livelock by writing the inodes to
> disk (maybe the xfssyncd) and the unmount then completed a couple
> of seconds later.
>
> From the above profile, I'm assuming that writeback_inodes_wb() was
> seeing pin_sb_for_writeback(sb) failing and moving dirty inodes from
> the the b_io to the b_more_io list, then being called again,
> splicing the inodes on b_more_io back to b_io, and then failed again
> to pin_sb_for_writeback() for each inode, moving them back to the
> b_more_io list....
>
> This is on 2.6.36-rc1 + the radix tree fixes for writeback.
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
> --
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>

--
Dave Chinner
david@fromorbit.com


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