linux-kernel - Re: [PATCH v8 11/12] zram: fix crashes with cpu hotplug multistate

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Message-ID: <YXGg95OcaR+5ktAZ@bombadil.infradead.org>
Date:   Thu, 21 Oct 2021 10:18:47 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, tj@...nel.org,
        gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
        minchan@...nel.org, jeyu@...nel.org, shuah@...nel.org,
        bvanassche@....org, dan.j.williams@...el.com, joe@...ches.com,
        tglx@...utronix.de, keescook@...omium.org, rostedt@...dmis.org,
        linux-spdx@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 11/12] zram: fix crashes with cpu hotplug multistate

On Thu, Oct 21, 2021 at 08:39:05AM +0800, Ming Lei wrote:
> On Wed, Oct 20, 2021 at 08:48:04AM -0700, Luis Chamberlain wrote:
> > A second series of tests is hitting CTRL-C on either randonly and
> > restarting testing once again randomly.
> 
> ltp/zram02.sh has cleanup handler via trap to clean everything(swapoff/umount/reset/
> rmmod), ctrl-c will terminate current forground task and cause shell to run the
> cleanup handler first, but further 'ctrl-c' will terminate the cleanup handler,
> then the cleanup won't be done completely, such as zram disk is left as swap
> device and zram can't be unloaded. The idea can be observed via the following
> script:
> 
> 	#!/bin/bash
> 	trap 'echo "enter trap"; sleep 20; echo "exit trap";' INT
> 	sleep 30
> 
> After the above script is run foreground, when 1st ctrl-c is pressed, 'sleep 30'
> is terminated, then the trap command is run, so you can see "enter trap"
> dumped. Then if you pressed 2nd ctrl-c, 'sleep 20' is terminated immediately.
> So 'swapoff' from zram02.sh's trap function can be terminated in this way.
> 
> zram disk being left as swap disk can be observed with your patch too
> after terminating via multiple ctrl-c which has to be done this way because
> the test is dead loop.
> 
> So it is hard to cleanup everything completely after multiple 'CTRL-C' is
> involved, and it should be impossible. It needs violent multiple ctrl-c to
> terminate the dealoop test.
> 
> So it isn't reasonable to expect that zram can be always unloaded successfully
> after the test script is terminated via multiple ctrl-c.

For the life of me, I do not run into these issue with my patch. But
with yours I had.

To be clear, I run zram02.sh on two terminals. Then to interrupt I just leave
CTRL-C pressed to issue multiple terminations until the script is done
on each terminal at a time, until I see both have completed.

I repeat the same test, noting always that when I start one one terminal
the test is succeeding. And also when I cancel completely one script the
test continue fine without issue.

> But zram can be unloaded after running swapoff manually, from driver
> viewpoint, nothing is wrong.

I had not run into that issue with my patch FWIW.

  Luis