linux-kernel - Re: [PATCH 1/3] firmware: Avoid superfluous usermodehelper lock

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Message-ID: <s5hd2t1wih4.wl%tiwai@suse.de>
Date:	Wed, 08 May 2013 18:21:11 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/3] firmware: Avoid superfluous usermodehelper lock

At Wed, 8 May 2013 23:52:02 +0800,
Ming Lei wrote:
> 
> On Wed, May 8, 2013 at 2:56 PM, Takashi Iwai <tiwai@...e.de> wrote:
> > When a firmware file can be loaded directly, there is no good reason
> > to lock usermodehelper.  It's needed only when the direct fw load
> > fails and falls back to the user-mode helper.
> 
> I remembered that we discussed the problem before, :-)
> 
> Some crazy drivers might call request_firmware inside resume callback
> (for example, USB devices might be rebind in resume), with
> usermodehelper_read_lock, we can find the mistake easily and log it.
> 
> I am wondering if it is good to remove the usermodehelper lock.
> 
> Could you let us know any benefit to do it?

Well, the question is whether usermodehelper lock is really an
appropriate stuff for *checking* the availability of direct fs
access.  I find it doesn't fit well any longer, in the situation where
no actual user-space call is needed.  Though, I'm not quite sure which
lock or flag can be used instead...


Takashi

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