linux-kernel - Re: [Merge tag 'pci-v4.12-changes' of git] 857f864014: BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8

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Message-ID: <20170614050112.GB11630@kroah.com>
Date:   Wed, 14 Jun 2017 07:01:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Sven-Haegar Koch <haegar@...net.de>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        kernel test robot <fengguang.wu@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKP <lkp@...org>, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, wfg@...ux.intel.com,
        Alan Cox <alan@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        David Herrmann <dh.herrmann@...il.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [Merge tag 'pci-v4.12-changes' of git] 857f864014: BUG: unable
 to handle kernel NULL pointer dereference at 00000000000000a8

On Tue, Jun 13, 2017 at 09:13:32PM +0200, Sven-Haegar Koch wrote:
> On Tue, 13 Jun 2017, Greg Kroah-Hartman wrote:
> 
> > On Tue, Jun 13, 2017 at 10:25:40AM -0600, Logan Gunthorpe wrote:
> > > 
> > > On 12/06/17 10:35 PM, Greg Kroah-Hartman wrote:
> > > > Or better yet, just turn all char major allocations into dynamic, which
> > > > would be really good for test systems.  I thought someone proposed
> > > > patches for that a long time ago, but I can't find them anymore.  That
> > > > would be the simplest solution here.
> > > 
> > > Would people not complain about that? I would not be surprised if some
> > > crazy application is using hard coded major numbers in userspace. So
> > > such a change could potentially break userspace...
> > 
> > For char devices, I doubt it, but we can't take the chance, which is why
> > you make it an option.  Then, it's enabled for 'allmodconfig' builds,
> > which helps testers out.
> 
> At least for /dev/null, /dev/zero, and perhaps /dev/tty it would 
> definitely break things if the major+minor number is not static. I have 
> multiple chroot environments having only some minimal needed static 
> /dev subdir, with naturally no daemons or filesystem creating those 
> on-demand. For the main /dev I use whatever the system sets up, so 
> devtmpfs with udev.

No, it wouldn't be required, it would be an option for those people
using devtmpfs.

thanks,

greg k-h