linux-kernel - Re: [PATCH v2 2/3] common/module: add patient module rmmod support

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Message-ID: <20210819022644.GP60846@e18g06458.et15sqa>
Date:   Thu, 19 Aug 2021 10:26:44 +0800
From:   Eryu Guan <eguan@...ux.alibaba.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Eryu Guan <guan@...u.me>, fstests@...r.kernel.org, hare@...e.de,
        dgilbert@...erlog.com, jeyu@...nel.org, lucas.demarchi@...el.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] common/module: add patient module rmmod support

On Wed, Aug 18, 2021 at 07:02:56AM -0700, Luis Chamberlain wrote:
> On Sun, Aug 15, 2021 at 08:29:42PM +0800, Eryu Guan wrote:
> > On Wed, Aug 11, 2021 at 08:45:11AM -0700, Luis Chamberlain wrote:
> > >  common/config |  31 +++++++++++++++
> > >  common/module | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++
> > 
> > Please also update README to document the new configurable variables.
> 
> Got it.
> 
> > >  2 files changed, 138 insertions(+)
> > > 
> > > diff --git a/common/config b/common/config
> > > index 005fd50a..9b8a2bc4 100644
> > > --- a/common/config
> > > +++ b/common/config
> > 
> > 100s as default seems a bit long to me, use 10s as in v1 patch?
> 
> In practice I tried using 10s and from my observations we *still* ran
> into false positives. So from my own testing peace of mind I'd prefer at
> least something higher, and if its going to be higher might as well go
> with something which at least makes painfully safe. I'll go with 50s
> for my next submission.
> 
> > > +	fi
> > > +else
> > > +	MODPROBE_RM_PATIENT_TIMEOUT_ARGS=""
> > > +	if [[ ! -z "$MODPROBE_PATIENT_RM_TIMEOUT_SECONDS" ]]; then
> > > +		if [[ "$MODPROBE_PATIENT_RM_TIMEOUT_MS" != "forever" ]]; then
> > 
> > Should check MODPROBE_PATIENT_RM_TIMEOUT_SECONDS instead?
> 
> Indeed will fix.
> 
> > > diff --git a/common/module b/common/module
> > > index 39e4e793..03953fa1 100644
> > > --- a/common/module
> > > +++ b/common/module
> > > @@ -4,6 +4,8 @@
> > >  #
> > >  # Routines for messing around with loadable kernel modules
> > >  
> > > +source common/config
> > > +
> > 
> > Seems there's no need to source common/config here, as it's sourced in
> > common/rc, which is sourced by every test.
> 
> OK.
> 
> > > +	local max_tries_max=$MODPROBE_PATIENT_RM_TIMEOUT_SECONDS
> <-- snip -->
> 
> > > +	local max_tries=0
> <-- snip -->
> 
> > > +	max_tries=$max_tries_max
> > > +
> > > +	while [[ "$max_tries" != "0" ]]; do
> > 
> > Use "$max_tries -ne 0" to check inters seems better.
> 
> max_tries can be "forever", in which case this is -eq 0:
> 
> $ foo="forever"; if [[ $foo -eq 0 ]]; then echo buggy; else echo ok; fi
> buggy

I see, that makes sense. Then perhaps some comments would help.

Thanks,
Eryu

> 
> > > +			refcnt_is_zero=1
> > > +			break
> > > +		fi
> > > +		sleep 1
> > > +		if [[ "$max_tries" == "forever" ]]; then
> > > +			continue
> > > +		fi
> > > +		let max_tries=$max_tries-1
> > > +	done
> > > +
> > > +	if [[ $refcnt_is_zero -ne 1 ]]; then
> > > +		echo "custom patient module removal for $module timed out waiting for refcnt to become 0 using timeout of $max_tries_max"
> > > +		return -1
> > > +	fi
> > > +
> > > +	# If we ran out of time but our refcnt check confirms we had
> > > +	# a refcnt of 0, just try to remove the module once.
> > > +	if [[ "$max_tries" == "0" ]]; then
> > 
> > $max_tries -eq 0
> 
> Same issue.
> 
>   Luis