On 11/16/21 09:29, Luis Chamberlain wrote:

A long time ago, in a galaxy far, far away...

I ran into some odd scsi_debug false positives with fstests. This
prompted me to look into them given these false positives prevents
me from moving forward with establishing a test baseline with high
number of cycles. That is, this stupid issue was prevening creating
high confidence in testing.

I reported it [0] and exchanged some ideas with Doug. However, in
the end, despite efforts to help things with scsi_debug there were
still issues lingering which seemed to defy our expectations upstream.
One of the last hanging fruit issues is and always has been that
userspace expectations for proper module removal has been broken,
so in the end I have demonstrated this is a generic issue [1].

Long ago a WAIT option for module removal was added... that was then
removed as it was deemed not needed as folks couldn't figure out when
these races happened. The races are actually pretty easy to trigger, it
was just never properly documented. A simpe blkdev_open() will easily
bump a module refcnt, and these days many thing scan do that sort of
thing.

The proper solution is to implement then a patient module removal
on kmod and patches have been sent for that and those patches are
under review. In the meantime we need a work around to open code a
similar solution for users of old versions of kmod. I sent an open
coded solution for fstests about since August 19th and has been used
there for a few months now. Now that that stuff is merged and tested
in fstests with more exposure, its time to match parity on blktests.

I've tested blktests with this for things which I can run virtually
for a while now. More wider testig is welcomed.

[0] https://bugzilla.kernel.org/show_bug.cgi?id=212337
[1] https://bugzilla.kernel.org/show_bug.cgi?id=214015
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

Thanks for having this work done and explaining the importance of it.

Give me couple of days, I'll provide you a feedback after I finish my
testing of your patch.