linux-kernel - Re: xfstests 073 regression

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Date:	Tue, 2 Aug 2011 20:16:01 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: xfstests 073 regression

On Tue, Aug 02, 2011 at 08:04:45PM +0800, Dave Chinner wrote:
> 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.
> 
> Right. We already kind of knew that was ocurring because there's
> a remount,ro going on.

Yes, and even better if it can be confirmed with a full sysrq-t trace.

> > 
> > > 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.
> 
> #define LOOP_MAJOR 7
> 
> It's a loop device. xfstests uses them quite a lot.

Yeah, it is.

> Maybe it would be a good idea to run xfstests on an xfs filesystem
> in your regular writeback testing cycle to get decent coverage of
> this case?

I've run xfstests case 073 on two of my boxes, however still cannot reproduce
the problem. This is the script I used, anything wrong with it?

        #!/bin/sh

        export TEST_DEV=/dev/sda5
        export TEST_DIR=/mnt/test

        export SCRATCH_DEV=/dev/sda6
        export SCRATCH_MNT=/mnt/scratch

        mount $TEST_DEV $TEST_DIR

        ./check 073

And the interesting thing is, that test case always fails in one box
and succeed in another.

Thanks,
Fengguang

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