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

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Date:   Fri, 2 Apr 2021 09:54:12 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     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
Subject: Re: [PATCH 1/2] zram: fix crashes due to use of cpu hotplug
 multistate

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.

Lock data, not code please.  Trying to tie data structure's lifespans
to the lifespan of code is a tangled mess, and one that I do not want to
add to in any form.

sorry,

greg k-h