Re: [PATCH 2/2] tests/xfs: test for post umount readahead completion panic

[Eryu Guan <eguan@redhat.com>]

On Fri, Jul 01, 2016 at 09:03:09AM -0400, Brian Foster wrote:
> On Fri, Jul 01, 2016 at 11:40:02AM +1000, Dave Chinner wrote:
> > On Thu, Jun 30, 2016 at 08:49:34AM -0400, Brian Foster wrote:
> > > XFS has a bug where directory readahead completions can occur after
> > > unmount. This can lead to a crash or panic because metadata read
> > > verification attempts to access core XFS data structures (e.g., the log)
> > > after they have been freed and certain pointers have been reset.
> > > 
> > > Add a test that triggers directory readahead, delays the readahead I/O
> > > and immediately unmounts the filesystem. This test is part of the
> > > dangerous group as it will cause kernels affected by the bug to crash.
> > .....
> > > +
> > > +# create a directory large enough for extent format
> > > +mkdir $SCRATCH_MNT/dir
> > > +for i in $(seq 0 999); do
> > > +	touch $SCRATCH_MNT/dir/$i
> > > +done
> > 
> > minor quibble - what's an "extent format" directory? I think you
> > mean a directory inode whose data fork is in extent or btree format,
> > not inline. i.e. not a short-form directory, but rather a block,
> > leaf or node format directory.
> > 
> 
> Indeed. So would you prefer the comment refers to the data fork or
> directory format? This really cares more about whether the directory has
> an extent count than the format per se, because that's what triggers the
> readahead.
> 
> Perhaps something like: "insert entries to grow the directory to at
> least one extent, which is what triggers readahead on dir open" ?
> 
> Eryu,
> 
> I'm assuming you can fix this up since you fixed up the previous patch.
> Let me know if you want me to send another version.

Sure, I can fix it. And I fixed the mount option issue Dave pointed out
in the dm-delay patch.

Thanks,
Eryu