From: Daniel Vetter <daniel@ffwll.ch>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Jörg Otte" <jrg.otte@gmail.com>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"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: Mon, 13 Jul 2015 08:22:22 +0200 [thread overview]
Message-ID: <20150713062222.GG3736@phenom.ffwll.local> (raw)
In-Reply-To: <CA+55aFxc=Xi1sjM+VFGw9ZR5-awgOy3VkE7goSuEdTJbYWfMGA@mail.gmail.com>
On Sun, Jul 12, 2015 at 09:52:51AM -0700, Linus Torvalds wrote:
> 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?
Indeed embarrassing. I've missed that we still have 1 caller left that's
using the transitional helpers, and those don't fill out
plane_state->state backpointers to the global atomic update since there is
no global atomic update for transitional helpers. Below diff should fix
this - we need to preferentially check crts_state->active and if that's
not set intel_crtc->active should yield the right result for the one
remaining caller (it's in the crtc_disable paths).
For cheap excuses why i915 is so crap in 4.2: Thanks to a hipshot decision
to transition to a different QA team ("we'll do this in 1 week without
upfront planing") I essentially don't have proper QA support for 1-2
months by now. The other trouble in this area specifically is that this
code is already completely changed in -next again, so any testing done on
integration trees (like -next or drm-intel-nightly) won't test any patches
for 4.2.
-Daniel
Oh and Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> in case you
decide to apply this right away.
---
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index ba9321998a41..85ac6d85dc39 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13276,7 +13276,7 @@ intel_check_primary_plane(struct drm_plane *plane,
if (ret)
return ret;
- if (crtc_state->base.active) {
+ if (crtc_state ? crtc_state->base.active : intel_crtc->active) {
struct intel_plane_state *old_state =
to_intel_plane_state(plane->state);
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2015-07-13 6:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-12 8:03 [4.2.0-rc1-00201-g59c3cb5] Regression: kernel NULL pointer dereference Jörg Otte
2015-07-12 16:33 ` Jörg Otte
2015-07-12 16:52 ` Linus Torvalds
2015-07-13 5:56 ` Maarten Lankhorst
2015-07-13 6:22 ` Daniel Vetter [this message]
2015-07-13 7:23 ` Maarten Lankhorst
2015-07-13 7:42 ` Jörg Otte
2015-07-13 7:58 ` Maarten Lankhorst
2015-07-13 8:50 ` Jörg Otte
2015-07-14 11:00 ` [PATCH] drm/i915: Do not call intel_crtc_disable if the crtc is already disabled Maarten Lankhorst
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