linux-kernel - Re: gadgetfs broken since 7f7f25e8

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Date:	Mon, 2 Mar 2015 10:20:32 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Richard Weinberger <richard.weinberger@...il.com>
Cc:	Alexander Holler <holler@...oftware.de>,
	USB list <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: gadgetfs broken since 7f7f25e8

On Mon, Mar 02, 2015 at 10:13:27AM +0100, Richard Weinberger wrote:
> On Mon, Mar 2, 2015 at 9:28 AM, Alexander Holler <holler@...oftware.de> wrote:
> > Hello.
> >
> > Commit 7f7f25e82d54870df24d415a7007fbd327da027b (introduced with 3.16) broke
> > dynamic changing of file_operations->[read|write].
> >
> > At least gadgetfs is a victim.
> >
> > Feel free to ask me off-list for a patch as I don't want to end up in
> > annoying discussions on Linux kernel lists anymore.
> >
> > Alexander Holler
> 
> CC'ing Al.

I know.  FWIW, gadgetfs is one of the very few places that tried to pull that
crap off and it had always been seriously racy.  I've posted a partial analysis
about a month ago (<20150204190645.GJ29656@...IV.linux.org.uk>).

If Alexander (or anybody else) has a patch that really fixes that thing,
I would certainly like to see it.  If not, I'll try to cook something,
but I'm not very familiar with that code.  I really hope that this patch
isn't "modify ->f_mode to match ->f_op change" - that's too racy.
We'll obviously need to fix the userland-visible breakage in that one,
but that's not the way to go...
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