linux-kernel - Re: [ANNOUNCE] kmod 30

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Message-ID: <Yr8zlqicFErzw0dc@bombadil.infradead.org>
Date:   Fri, 1 Jul 2022 10:49:10 -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 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`?

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
}

> > 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.

So just a heads up the timeout I'll use for fstests / blktests will be
of 100 seconds.

Thanks for this work!

  Luis