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

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Date:	Wed, 08 May 2013 18:37:01 +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, 08 May 2013 18:21:11 +0200,
Takashi Iwai wrote:
> 
> 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...

In other words, the first patch is no essential part of the fix.
I can revisit the second patch without this one and resend if
preferred.


Takashi
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