Re: [whacky issue] xfs/277 endlessly looping in _require_xfs_io_command

[Brian Foster <bfoster@redhat.com>]

On Wed, Oct 11, 2017 at 07:00:47PM +1100, Dave Chinner wrote:
> HI folks,
> 
> I was wondering if anyone else had seen this problem, because it's
> got me absolutely stumped. One of my test VMs is having a really
> weird livelock in xfs/277. It's getting stuck in an endless loop
> burning the entire CPU in a the 277 process (i.e. running bash).
> What it is stuck on makes no sense to me, nor does the looping
> behaviour, and I can only reproduce it on this one machine.
> 
> The code in question:
> 
>         "fsmap" )
>                 testio=`$XFS_IO_PROG -f -c "fsmap" $testfile 2>&1`
>                 echo $testio | grep -q "Inappropriate ioctl" && \
>                         _notrun "xfs_io $command support is missing"
> 

Oh, so it looks like you're in _require_xfs_io_command(). I was hunting
around for this code in xfs/277. :P

> Is pretty simple and obvious - not a lot to go wrong. set -x
> shows the last command in the output file to be the fsmap command.
> $test_io has about 5000 lines of output in it.
> 
> I did some testing to isolate the problem. This exits having
> executed the fsmap command just fine:
> 
> 
>         "fsmap" )
>                 testio=`$XFS_IO_PROG -f -c "fsmap" $testfile 2>&1`
>                 exit
> 
> But this never exits and it starts burning down teh CPU:
> 
>         "fsmap" )
>                 testio=`$XFS_IO_PROG -f -c "fsmap" $testfile 2>&1`
>                 echo $testio
>                 exit
> 
> Yeah, echoing the output of the fsmap command seems to cause bash to
> enter an endless loop of some kind. Well, it's not endless, because
> every 30s or so the process dies and a new child process runs the
> same loop again. Attaching strace to one of these processes:
> 
...
> 
> bash is running around in a tight loop running readdir() on some
> unknown directory over and over again. I can't work it out - this is
> the only machine that does it, and it I can't reproduce it outside
> of running xfs/277 from xfstests...
> 
> I'm outta ideas - I've got no idea what the hell is going wrong
> here. Anyone got any ideas?
> 

Heh, that sounds pretty strange. Does your test dev have a pre-existing
$testfile? Have you tried to execute the associated code in an
independent bash script? E.g., I'd probably try to do something like
mount your test dev then run:

	XFS_IO_PROG=...
	testfile=...

	testio=`$XFS_IO_PROG -f -c "fsmap" $testfile 2>&1`
	echo $testio

... from a separate script using hardcoded values from the xfstests
environment, and see what happens..?

Brian

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> --
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