linux-kernel - Re: [PATCH v2 1/3] firmware loader: Introduce new API

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Message-ID: <20141108190655.GA2638@kroah.com>
Date:	Sat, 8 Nov 2014 11:06:55 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Kweh Hock Leong <hock.leong.kweh@...el.com>
Cc:	Matt Fleming <matt.fleming@...el.com>,
	Ming Lei <ming.lei@...onical.com>,
	Sam Protsenko <semen.protsenko@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-efi@...r.kernel.org,
	Ong Boon Leong <boon.leong.ong@...el.com>
Subject: Re: [PATCH v2 1/3] firmware loader: Introduce new API -
 request_firmware_abort()

On Mon, Nov 03, 2014 at 11:07:08AM +0800, Kweh Hock Leong wrote:
> From: "Kweh, Hock Leong" <hock.leong.kweh@...el.com>
> 
> Besides aborting through user helper interface, a new API
> request_firmware_abort() allows kernel driver module to abort the
> request_firmware() / request_firmware_nowait() when they are no
> longer needed. It is useful for cancelling an outstanding firmware
> load if initiated from inside a module where that module is in the
> process of being unloaded, since the unload function may not have
> a handle to the struct firmware_buf.
> 
> Note for people who use request_firmware_nowait():
> You are required to do your own synchronization after you call
> request_firmware_abort() in order to continue unloading the
> module. The example synchronization code shows below:
> 
> while (THIS_MODULE && module_refcount(THIS_MODULE))
> 	msleep(20);

As others have pointed out, this isn't ok, and is totally racy and
should never end up in a driver.  Never mess with THIS_MODULE from
within the same module, otherwise it's racy and broken code.

So can you please rework this to not require this?

thanks,

greg k-h
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