Re: [PATCH] blktests: replace module removal with patient module removal

[Luis Chamberlain <mcgrof@kernel.org>]

On Wed, Dec 08, 2021 at 04:53:04AM -0800, Luis Chamberlain wrote:
> On Thu, Nov 18, 2021 at 01:38:49AM +0000, Chaitanya Kulkarni wrote:
> > 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.
> 
> How did testing go?

*Friendly poke*

  Luis