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

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Date:   Tue, 19 Oct 2021 12:38:42 -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 Wed, Oct 20, 2021 at 12:39:22AM +0800, Ming Lei wrote:
> On Tue, Oct 19, 2021 at 08:50:24AM -0700, Luis Chamberlain wrote:
> > So do you want to take the position:
> > 
> > Hey driver authors: you cannot use any shared lock on module removal and
> > on sysfs ops?
> 
> IMO, yes, in your patch of 'zram: fix crashes with cpu hotplug multistate',
> when you added mutex_lock(zram_index_mutex) to disksize_store() and
> other attribute show() or store() method. You have added new deadlock
> between hot_remove_store() and disksize_store() & others, which can't be
> addressed by your approach of holding module refcnt.
> 
> So far not see ltp tests covers hot add/remove interface yet.

Care to show what commands to use to cause this deadlock with my patches?

  Luis