Re: first it froze, now the (btrfs) root fs won't mount ...

[Christian Pernegger <pernegger@gmail.com>]

[Please CC me, I'm not on the list.]

Am Mo., 21. Okt. 2019 um 13:47 Uhr schrieb Austin S. Hemmelgarn
<ahferroin7@gmail.com>:
> I've [worked with fs clones] like this dozens of times on single-device volumes with exactly zero issues.

Thank you, I have taken precautions, but it does seem to work fine.

> There are actually two possible ways I can think of a buggy GPU driver causing this type of issue: [snip]

Interesting and plausible, but ...

> Your best option for mitigation [...] is to ensure that your hardware has an IOMMU [...] and ensure it's enabled in firmware.

It has and it is. (The machine's been specced so GPU pass-through is
an option, should it be required. I haven't gotten around to setting
that up yet, haven't even gotten a second GPU, but I have laid the
groundwork, the IOMMU is enabled and, as far as one can tell from logs
and such, working.)

> However, there's also the possibility that you may have hardware issues.

Don't I know it ... The problem is, if there are hardware issues,
that's the first I've seen of them, and while I didn't run torture
tests, there was quite a lot of benchmarking when it was new. Needle
in a haystack. Some memory testing can't hurt, I suppose. Any other
ideas (for hardware testing)?

Back on the topic of TRIM: I'm 99 % certain discard wasn't set on the
mount (not by me, in any case), but I think Mint runs fstrim
periodically by default. Just to be sure, should any form of TRIM be
disabled?
The only other idea I've got is Timeshift's hourly snapshots. (How)
would btrfs deal with a crash during snapshot creation?


In other news, I've still not quite given up, mainly because the fs
doesn't look all that broken. The output of btrfs inspect-internal
dump-tree (incl. options), for instance, looks like gibberish to me of
course, but it looks sane, doesn't spew warnings, doesn't error out or
crash. Also plain btrfs check --init-extent-tree errored out, same
with -s0, but with -s1 it's now chugging along. (BTW, is there a
hierarchy among the super block slots, a best or newest one?)

Will keep you posted.

Cheers,
C.