linux-kernel - Re: [PATCH v3 2/3] zram: fix deadlock with sysfs attribute usage and driver removal

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Message-ID: <YNGUIzh7aR3C/Hoz@kroah.com>
Date:   Tue, 22 Jun 2021 09:41:23 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     minchan@...nel.org, jeyu@...nel.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com, axboe@...nel.dk,
        mbenes@...e.com, jpoimboe@...hat.com, tglx@...utronix.de,
        keescook@...omium.org, jikos@...nel.org, rostedt@...dmis.org,
        peterz@...radead.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] zram: fix deadlock with sysfs attribute usage and
 driver removal

On Mon, Jun 21, 2021 at 04:36:34PM -0700, Luis Chamberlain wrote:
> +	ssize_t __ret; \
> +	if (!try_module_get(THIS_MODULE)) \

try_module_get(THIS_MODULE) is always racy and probably does not do what
you want it to do.  You always want to get/put module references from
code that is NOT the code calling these functions.

> +		return -ENODEV; \
> +	__ret = _name ## _store(dev, attr, buf, len); \
> +	module_put(THIS_MODULE); \

This too is going to be racy.

While fun to poke at, I still think this is pointless.

greg k-h