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

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Date:   Thu, 8 Apr 2021 08:18:21 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
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 Wed, Apr 07, 2021 at 03:17:46PM -0500, Josh Poimboeuf wrote:
> 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.

My throw-away comment here seems to have gotten way more attention than
it deserved, sorry about that everyone.

Nothing is supported for anything here, it's all "best effort" :)

And I would love a taint for rmmod, but what is that going to help out
with?

thanks,

greg k-h