linux-kernel - Re: [lkp] [gpio] 3c702e9987: kmsg.user_verbs:couldn't_register_device

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Date:	Sun, 14 Feb 2016 11:05:15 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Michael Welling <mwelling@...e.org>,
	Roland Dreier <rolandd@...co.com>,
	kernel test robot <ying.huang@...ux.intel.com>, lkp@...org,
	LKML <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Markus Pargmann <mpa@...gutronix.de>,
	Johan Hovold <johan@...nel.org>
Subject: Re: [lkp] [gpio] 3c702e9987:
 kmsg.user_verbs:couldn't_register_device_number

On Sun, Feb 14, 2016 at 06:56:20PM +0100, Linus Walleij wrote:
> On Sun, Feb 14, 2016 at 6:49 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> > On Sun, Feb 14, 2016 at 06:42:11PM +0100, Linus Walleij wrote:
> >> Greg, heads-up on this... you'd know if this happened
> >> before.
> >>
> >> On Sun, Feb 14, 2016 at 9:06 AM, Michael Welling <mwelling@...e.org> wrote:
> >> > On Sun, Feb 14, 2016 at 02:59:06PM +0800, kernel test robot wrote:
> >> >> FYI, we noticed the below changes on
> >> >>
> >> >> https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio.git chardev
> >> >> commit 3c702e9987e261042a07e43460a8148be254412e ("gpio: add a userspace chardev ABI for GPIOs")
> >> >>
> >> >>
> >> >> [    1.951191] user_verbs: couldn't register device number
> >> >
> >> > Looks like user_verbs is using a static device node setup.
> >> >
> >> > enum {
> >> >         IB_UVERBS_MAJOR       = 231,
> >> >         IB_UVERBS_BASE_MINOR  = 192,
> >> >         IB_UVERBS_MAX_DEVICES = 32
> >> > };
> >> >
> >> > #define IB_UVERBS_BASE_DEV      MKDEV(IB_UVERBS_MAJOR, IB_UVERBS_BASE_MINOR)
> >>
> >> That's annoying...
> >> I notice that infiniband is using register_chrdev_region() at
> >> module_init() time, counting on device major 231 to be free.
> >
> > That device major is assigned to Infiniband, why shouldn't it be doing
> > this?
> 
> I mean it's annoying that they collide. (Because of the details I
> write below, it's fine it's using the assigned number.
> 
> > Why not just ask for a new reserved one?  We could give you 261 and
> > everything should be fine, right?
> 
> Sure I can post a patch for that, but it just mitigates the problem.
> 
> The report point to the serious problem that on this system
> some dynamic allocations have already stolen major device
> numbers 232 thru 255, and 232 and 233 are also assigned.
> 
> What do you think about a patch that makes fs/char_dev.c
> emit a warning when it starts assigning dynamic numbers
> 233 and below?

That's fine with me.  I also think maybe we should look into just
switching all char major/minor allocation to be dynamic, starting at the
bottom and moving up.  I think the only tools that might have an issue
with that is the raw device controller, but maybe that has been fixed up
in userspace, I haven't looked at that in many years.

I thought I had an old patch around somewhere that did that, will go
look for it this week and see what breaks with it enabled...

thanks,

greg k-h