linux-kernel - Re: [PATCH 1/2] zram: fix crashes due to use of cpu hotplug multistate

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Message-ID: <20210407201746.ueijmegmpbyq5quv@treble>
Date:   Wed, 7 Apr 2021 15:17:46 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Minchan Kim <minchan@...nel.org>, keescook@...omium.org,
        dhowells@...hat.com, hch@...radead.org, mbenes@...e.com,
        ngupta@...are.org, sergey.senozhatsky.work@...il.com,
        axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jessica Yu <jeyu@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] zram: fix crashes due to use of cpu hotplug
 multistate

On Fri, Apr 02, 2021 at 09:54:12AM +0200, Greg KH wrote:
> On Thu, Apr 01, 2021 at 11:59:25PM +0000, Luis Chamberlain wrote:
> > As for the syfs deadlock possible with drivers, this fixes it in a generic way:
> > 
> > commit fac43d8025727a74f80a183cc5eb74ed902a5d14
> > Author: Luis Chamberlain <mcgrof@...nel.org>
> > Date:   Sat Mar 27 14:58:15 2021 +0000
> > 
> >     sysfs: add optional module_owner to attribute
> >     
> >     This is needed as otherwise the owner of the attribute
> >     or group read/store might have a shared lock used on driver removal,
> >     and deadlock if we race with driver removal.
> >     
> >     Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> 
> No, please no.  Module removal is a "best effort", if the system dies
> when it happens, that's on you.  I am not willing to expend extra energy
> and maintance of core things like sysfs for stuff like this that does
> not matter in any system other than a developer's box.

So I mentioned this on IRC, and some folks were surprised to hear that
module unloading is unsupported and is just a development aid.

Is this stance documented anywhere?

If we really believe this to be true, we should make rmmod taint the
kernel.

-- 
Josh