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

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Message-ID: <YG3iQ82gYkcp4G5Q@hirez.programming.kicks-ass.net>
Date:   Wed, 7 Apr 2021 18:48:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Miroslav Benes <mbenes@...e.cz>,
        Greg KH <gregkh@...uxfoundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>, mbenes@...e.com,
        Minchan Kim <minchan@...nel.org>, keescook@...omium.org,
        dhowells@...hat.com, hch@...radead.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org, Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH 1/2] zram: fix crashes due to use of cpu hotplug
 multistate

On Wed, Apr 07, 2021 at 10:30:31AM -0500, Josh Poimboeuf wrote:
> On Wed, Apr 07, 2021 at 04:09:44PM +0200, Peter Zijlstra wrote:
> > On Tue, Apr 06, 2021 at 10:54:23AM -0500, Josh Poimboeuf wrote:
> > 
> > > Same for Red Hat.  Unloading livepatch modules seems to work fine, but
> > > isn't officially supported.
> > > 
> > > That said, if rmmod is just considered a development aid, and we're
> > > going to be ignoring bugs, we should make it official with a new
> > > TAINT_RMMOD.
> > 
> > Another option would be to have live-patch modules leak a module
> > reference by default, except when some debug sysctl is set or something.
> > Then only those LP modules loaded while the sysctl is set to 'YOLO' can
> > be unloaded.
> 
> The issue is broader than just live patching.
> 
> My suggestion was that if we aren't going to fix bugs in kernel module
> unloading, then unloading modules shouldn't be supported, and should
> taint the kernel.

Hold up, what? However much I dislike modules (and that is lots), if you
don't want to support rmmod, you have to leak a reference to self in
init. Barring that you get to fix any and all unload bugs.