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: <CACRpkdZyup+dH6Yp747yLyaC8DSbA8bEnk37gJKnmnjBvjn=-A@mail.gmail.com>
Date:   Wed, 14 Jun 2017 11:59:29 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        "linux-kernel@...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>,
        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 6:34 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:

> Ah, that makes sense.  Well, someone can always work on expanding the
> range of dynamic char major numbers if they are running out of them on a
> real system, I'll gladly take patches for that :)

I started to take a stab at it at one point and incorporated some feedback
from Torvalds etc, it's here:
https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio.git/commit/?h=chrdev-warn&id=65e5b1e9eb3f777ab7535b74b490e882eeec79d7

It tries to use all "holes" in the chardev major map to shun in a bit
more devices when we run out of the high dynamic major range.

Making them all dynamic seemed dangerous because I was afraid
of userspace ABI breakage because of old userlands with
static mknod:s.

I lost interest when it turned out that the zeroday QEMU stuff was
generating random machines that have no counterpart in the real
world, and then the exercise seemed a bit academic.

The last failures were due to (AFAICT) some relationship between
major and minor numbers that I didn't untangle.

If there is interest I could try to revive it.

Yours,
Linus Walleij