VFS_BIO_DEBUG and 4.11

[Stephen McKay]

Hi-diddly-ho!

Is VFS_BIO_DEBUG still supposed to work in 4.11?  I'm trying to debug a
data corruption problem that could be a bug in the cd9660 file system and
thought that enabling VFS_BIO_DEBUG might help.  Instead it complains a
lot about directories and character devices being VMIO'd nowadays, then
panics with "biodone: zero vnode ref count" before it even finishes
booting.

I have reason to believe this was a useful flag back in 4.4 (because I
saw a kernel config from Matt Dillon that included it), but have not found
any evidence of use more recent than that.

So, is it obsolete now?  Or is it just only a little bit broken?  I don't
(yet) understand the invariants it is trying to enforce, so perhaps none
of them apply any more.

Stephen.