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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