Re: [PATCH v2] btrfs: reject refs=0 subvolume without DEAD in SUBVOL_SYNC_WAIT

[Cheng Yongkang <teel4res@gmail.com>]

Hi Qu,

Thanks for taking the time to list these.

To be upfront about where this came from: I work on automated bug
finding for the kernel, and this ASSERT was one of its findings; the
analysis and the patch were LLM-assisted. I sent a fix rather than a
bare report because I had the impression that reports without a fix
get little attention, but I'm not the right person to rework
SUBVOL_SYNC_WAIT and add the btrfs-progs support and test cases you
describe.

One data point on the return value: in my testing on for-next, waiting
for a subvolume that was being deleted returned -ENOENT once the
cleaner had removed it, with and without this patch, so the success
path is never reached.

Since the tool keeps finding issues like this, I'd like to ask how you
would prefer to receive them:

- Would a [BUG] report with a reproducer, the tree and config, the
  trace and a short analysis be more useful to you than a patch I
  can't take further?
- For low-priority cases like this one (a debug-only ASSERT in an
  ioctl with no real users), would you rather I batch them, or not
  send them at all?

If the ASSERT fix alone is still useful, I can send a v3 that only
replaces it with -EUCLEAN. Otherwise I'm fine with dropping the patch
and leaving this as a report.

Thanks,
Cheng Yongkang