linux-kernel - Re: [ANNOUNCE] kmod 30

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Date:   Fri, 1 Jul 2022 11:13:21 -0700
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
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 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"

>
>> > 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.

>
>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


Lucas De Marchi

>
>Thanks for this work!
>
>  Luis