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

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Message-ID: <20210407145251.GD4332@42.do-not-panic.com>
Date:   Wed, 7 Apr 2021 14:52:51 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     keescook@...omium.org, dhowells@...hat.com, hch@...radead.org,
        mbenes@...e.com, gregkh@...uxfoundation.org, 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 Tue, Apr 06, 2021 at 06:38:24PM -0700, Minchan Kim wrote:
> To clarify what I understood form the discussion until now:
> 
> 1. zram shouldn't allow creating more zram instance during
> rmmod(It causes CPU multistate splat)

Right!

> 2. the private data of gendisk shouldn't destroyed while zram
> sysfs knob is working(it makes system goes crash)

Yup, this is resolved with the bdgrab / bdput on each sysfs knob.

And the last issue is:

3) which patch 2/2 addresed. If a mutex is shared on sysfs
knobs and module removal, you must do try_module_get() to prevent
the deadlock.

  Luis