linux-kernel - Re: [PATCH v5 1/5] firmware: document user mode helper lock usage

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Date:   Wed, 5 Oct 2016 22:46:28 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Daniel Wagner <daniel.wagner@...-carit.de>
Cc:     Ming Lei <ming.lei@...onical.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Daniel Wagner <wagi@...om.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "rafael.j.wysocki" <rafael.j.wysocki@...el.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Takashi Iwai <tiwai@...e.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Arend van Spriel <arend.vanspriel@...adcom.com>
Subject: Re: [PATCH v5 1/5] firmware: document user mode helper lock usage

On Fri, Sep 23, 2016 at 10:13:44AM +0200, Daniel Wagner wrote:
> On 09/22/2016 04:36 AM, Ming Lei wrote:
> >On Sat, Sep 10, 2016 at 6:14 AM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> >>On Fri, Sep 09, 2016 at 02:12:20PM +0200, Daniel Wagner wrote:
> >>>From: Daniel Wagner <daniel.wagner@...-carit.de>
> >>>
> >>>The lock is also used to generate warnings when a direct
> >>>firmware load is requested too early.
> >>
> >>I've determined the firmware cache lets us bail out of this
> >>consideration now. If Ming agrees with the logic we don't need this
> >>patch and you can continue as you had intended. Sorry for the trouble.
> >
> >IMO it is helpful to add comment about using the lock for direct loading,
> >and we can sort it out in future if anyone want to improve it.
> >
> >So for this patch, I am fine.
> 
> Sorry, I am a bit confused now. What is the consensus here:
> 
>  a) add a comment to _request_firmware() as in this patch #1 v5

The adding a comment note from Daniel was that the UMH lock is *not*
needed on the direct firmware loading case, he's lazy to remove it
now so he'll just add a comment.

>  b) move the umh locking to fw_load_from_user_helper() as in
>     patch #1 v4

This is fine and IMHO the non-lazy approach.

To be clear -- I did my own vetting of the removal of the lock by
inspecting the original purpose of the UMH lock being added on the
history Linux git tree, having a secondary review of that would be
appreciated as well.

  Luis