linux-kernel - Re: [ANNOUNCE] kmod 30

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Date:   Fri, 1 Jul 2022 14:25:27 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Lucas De Marchi <lucas.demarchi@...el.com>
Cc:     linux-modules <linux-modules@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [ANNOUNCE] kmod 30

On Fri, Jul 01, 2022 at 11:13:21AM -0700, Lucas De Marchi wrote:
> On Fri, Jul 01, 2022 at 10:49:10AM -0700, Luis Chamberlain wrote:
> > On Thu, Jun 30, 2022 at 03:33:23PM -0700, Lucas De Marchi wrote:
> > > On Thu, Jun 30, 2022 at 03:09:32PM -0700, Luis Chamberlain wrote:
> > > > Sorry for the super late review, I was swamped. OK so the only issue
> > > > I can think of is that rmmod *used* to support the kernel wait support
> > > > with $(rmmod --wait) so wouldn't this be odd?
> > > 
> > > any reason not to use modprobe -r?
> > 
> > I was referring to old scripts which may have used $(rmmod --wait) before.
> > But since support for that was ripped, then yeah I can see that should
> > not be an issue.
> > 
> > However I can think of *one* issue, did we ever support `modprobe--wait`?
> 
> no
> 
> > 
> > Because the way fstests / blktests would implement this feature
> > detection is with something like this now:
> > 
> > _has_modprobe_patient()
> > {
> > 	modprobe --help >& /dev/null || return 1
> > 	modprobe --help | grep -q -1 "remove-patiently" || return 1
> > 	return 0
> > }
> 
> the grep would need to be changed to something like "-w, --wait"

Yes of course, that's easy, but we modprobe ever supportedl "--wait"
this would be a problem. Since it did not, we are good then!

> > > > It is why I had gone with:
> > > >
> > > > -p | --remove-patiently   patiently removes the module
> > > > -t | --timeout            timeout in ms to remove the module
> > > >
> > > > You would know better though.
> > > >
> > > > Also just curious, is it really terrible to just support waiting
> > > > forever?
> > > 
> > > is there a use case for that? If we are trying to cover some races, I
> > > imagine a small timeout would be sufficient. Also notice that if the
> > > timeout is too big, so will be the interval between the retries.  On
> > > your v2 I had suggested polling the refcnt so we would get notificed
> > > on changes, but as you also noticed, that didn't work very well.  So I
> > > went back to a time-based retry solution.
> > > 
> > > if there is a use-case, should we cap the interval between retries?
> > 
> > I really can't think of a use case except for catching glaring
> > unexpected bugs in test suites where the kernel developer would
> > really like to know something really bad happened, but even then
> > a timeout is likely desirable.
> 
> yeah... if developer wants to possibly wait for a long time, `--wait -1`
> is available to wait for years.

:) good call

> > So just a heads up the timeout I'll use for fstests / blktests will be
> > of 100 seconds.
> 
> yeah... 100 seconds still make more sense than -1 IMO

Great we'll go with that. Hopefully this will put a nail on the flaky
modules issue for good!

  Luis