Hey,
> Taking a quick look at something I have laying around that you sent
> previously (I assume the test hasn't changed much), I see we basically
> create an overprovisioned dm-thin vol, mount it and dio write to it
> until we start to see async write failures. So is the purpose of the
> wait that we need the AIL to push and ultimately fail the associated
> buffers before we attempt an unmount? If so, I'm wondering if you could
> xfs_freeze the fs rather than wait (it looks like freeze sync pushes the
> AIL)..?
>
As we discussed off-list, yes, I'd done some testing, and I believe we can use
freezing to test it.
> > > >
> > > > I think we all agree that generic error injection (which Darrick has
> > > > started playing with, but I haven't looked at yet) doesn't need to be
> > > > bundled with this series (I hope we didn't scare you there ;). What I
> > > > was asking for is a single patch that adds error injection in one spot
> > > > with a configurable frequency. I'll refer to commit 609adfc2ed ("xfs:
> > > > debug mode log record crc error injection") again because it is a simple
> > > > example of a small DEBUG only hunk of code and boilerplate code to add a
> > > > sysfs knob.
> > > >
> >
> > I'll keep this in mind, and try to work on something like that :)
> >
>
> I think error injection would make this test more straightforward
> because you can explicitly control when I/Os fail and there's no need to
> play around with dm-thin. That of course doesn't mean there isn't value
> in having a test for fs' in dm-thin out of space conditions in general.
> :)
Well, this is doable, although it has a caveat.
To do this, we'd need to inject the error in the buffer during IO completion,
for example in xfs_buf_ioend(). The problem though, is that we start to have IOs
before the 'mp->m_errotag' is actually initialized, so, xfs_buf_ioend() would
need to check for m_errortag initialization before calling XFS_TEST_ERROR().
Something like this:
bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD);
+ if (bp->b_target->bt_mount->m_errortag) {
+ if (XFS_TEST_ERROR(false, bp->b_target->bt_mount,
+ XFS_ERRTAG_BUF_WB)) {
+ bp->b_io_error = -ENOSPC;
+ }
+ }
This check could also be done in xfs_errortag_test(), although I'm not sure if
it's worth, giving that there are very few places where error injection can be
useful and m_errortag can be uninitialized.
Thoughts?
--
Carlos
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