linux-kernel - Re: [2.6.36-rc1] unmount livelock due to racing with bdi-flusher threads

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Date:	Mon, 13 Sep 2010 12:41:28 +1000
From:	Dave Chinner <david@...morbit.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-fsdevel@...r.kernel.org
Subject: Re: [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@...morbit.com
> --
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> 

-- 
Dave Chinner
david@...morbit.com
--
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