[Bug 200981] hypervisor fs hangs at heavy write activity on VM (kvm, qcow2 image) having a reflink disk copy

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https://bugzilla.kernel.org/show_bug.cgi?id=200981

--- Comment #8 from Dave Chinner (david@fromorbit.com) ---
(In reply to Alexander Y.  Fomichev from comment #7)
> Ok, it looks like a warning is a result of missing y in
> xfs_reflink_allocate_cow, namely in a sequence xfs_trans_alloc -> goto retry
> -> goto convert.

Yup, I see the issue. Nice work finding this!

> With proof-of-concept patch (attached) warning is gone but
> deadlock is not.

The code is not missing a sb_end_intwrite() call - it's missing a
xfs_trans_cancel() call. That's why it still deadlocks even though you shut up
the warning. I'll have a closer look in the morning to see if there's any other
paths that can leak the transaction and write a patch to fix it.

Thanks again for tracking it down, Alexander :)

Cheers,

Dave.

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