Re: [4.2.0-rc1-00201-g59c3cb5] Regression: kernel NULL pointer dereference

From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Jörg Otte" <jrg.otte@gmail.com>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>,
	DRI <dri-devel@lists.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Subject: Re: [4.2.0-rc1-00201-g59c3cb5] Regression: kernel NULL pointer dereference
Date: Sun, 12 Jul 2015 09:52:51 -0700	[thread overview]
Message-ID: <CA+55aFxc=Xi1sjM+VFGw9ZR5-awgOy3VkE7goSuEdTJbYWfMGA@mail.gmail.com> (raw)
In-Reply-To: <CADDKRnB8D3H_61BCe1gD7TXQt1eRniGTfqPESnK0jM4HE16oCg@mail.gmail.com>

On Sun, Jul 12, 2015 at 1:03 AM, Jörg Otte <jrg.otte@gmail.com> wrote:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000009
> IP: [<ffffffffbd3447bb>] 0xffffffffbd3447bb

Ugh. Please enable KALLSYMS to get sane symbols.

But yes, "crtc_state->base.active" is at offset 9 from "crtc_state",
so it's pretty clearly just that change frm

-       if (intel_crtc->active) {
+       if (crtc_state->base.active) {

and "crtc_state" is NULL.

And the code very much knows that crtc_state can be NULL, since it's
initialized with

        crtc_state = state->base.state ?
                intel_atomic_get_crtc_state(state->base.state,
intel_crtc) : NULL;

Tssk. Daniel? Should I just revert that commit dec4f799d0a4
("drm/i915: Use crtc_state->active in primary check_plane func") for
now, or is there a better fix? Like just checking crtc_state for NULL?

                    Linus