From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: xfstests 073 regression
Date: Tue, 2 Aug 2011 20:05:52 +0800
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Cc: Dave Chinner <david@fromorbit.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jan Kara <jack@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
To: Christoph Hellwig <hch@infradead.org>
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On Tue, Aug 02, 2011 at 07:44:28PM +0800, Wu Fengguang wrote:
> On Tue, Aug 02, 2011 at 12:52:42AM +0800, Christoph Hellwig wrote:
> > wb_check_background_flush is indeed what we're hitting.
> 
> That means s_umount is NOT held by another queued writeback work.
> 
> > See the trace output using a patch inspired by Curt's below:
> > 
> > # tracer: nop
> > #
> > #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> > #              | |       |          |         |
> >            <...>-4279  [000]   113.034052: writeback_grab_super_failed: bdi 7:0: sb_dev 0:0 nr_pages=9223372036854775807 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=wb_check_background_flush
> >            <...>-4279  [000]   113.034052: writeback_grab_super_failed: bdi 7:0: sb_dev 0:0 nr_pages=9223372036854775807 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=wb_check_background_flush
> >            <...>-4279  [000]   113.034052: writeback_grab_super_failed: bdi 7:0: sb_dev 0:0 nr_pages=9223372036854775807 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=wb_check_background_flush
> 
> What's that bdi 7:0? And sb_dev=0:0, nr_pages=9223372036854775807=0x7fffffffffffffff.
> 
> All are indicating some special bdi/inode.

I see, it's loop0:

lrwxrwxrwx 1 root root 0 Aug  2 20:46 /sys/class/block/loop0/bdi -> ../../bdi/7:0

Thanks,
Fengguang