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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Date:   Tue, 13 Jun 2017 23:55:37 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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 13/06/17 11:00 PM, Greg Kroah-Hartman wrote:
> No, don't modify any drivers, do this in the core chardev code.

Ok, well then maybe I misunderstood what you originally asked for
because I don't see how you can change a fixed allocation to a dynamic
one without touching the driver code which needs to know the major that
was assigned in the end.

> At quick glance, looks good to me, care to clean it up and make it behind
> a config option?

Sure. However, is a config option really necessary here? As is, the
extended dynamic region will only be used if there are too many chardev
majors and it shouldn't have _any_ effect on users that have a small
number. So it seems like not selecting that option is just telling the
kernel to be broken for no obvious trade-off.

Logan