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

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Message-ID: <YW7xbnrqfzifa9OC@kroah.com>
Date:   Tue, 19 Oct 2021 18:25:18 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Ming Lei <ming.lei@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, tj@...nel.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 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?

Yes, I would not recommend using such a lock at all.  sysfs operations
happen on a per-device basis, so you can lock the device structure.
Module removal happens on a driver basis, and I have no idea what you
want to lock there, but odds are it is NOT shared with your per-device
structures either, right?

If so, then yes, that is a bug, but a very rare one as drivers should do
almost nothing except register/unregister_driver() in their module
init/exit calls.

zram is not a "normal" driver at all here, so fixing this type of
problem up should be done in the zram code, it is not a generic
module/sysfs issue at all.

thanks,

greg k-h