When the subtest basic-plain-flip from IGT project was executed on Bochs
driver, the following bug appears:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD 0 P4D 0
Oops: 0010 [#1] PREEMPT SMP PTI
CPU: 0 PID: 423 Comm: kms_flip Not tainted 5.0.0-VM+ #102
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014
RIP: 0010: (null)
Code: Bad RIP value.
RSP: 0018:ffffb6a6c0bdfb70 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff90467940bf00 RCX: ffff90467a730318
RDX: 000000000000001f RSI: 0000000000000003 RDI: ffff90467bf94050
RBP: ffff90467bf94050 R08: ffff904679424e00 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000000
R13: ffff90467a460000 R14: ffff90467946d400 R15: ffffffffc080d460
FS: 00007f259c1990c0(0000) GS:ffff90467c800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000b97ec000 CR4: 00000000000006f0
Call Trace:
? drm_atomic_helper_commit_modeset_disables+0x396/0x3e0 [drm_kms_helper]
? drm_atomic_helper_commit_tail+0x19/0x60 [drm_kms_helper]
? commit_tail+0x58/0x70 [drm_kms_helper]
? drm_atomic_helper_commit+0x103/0x110 [drm_kms_helper]
? drm_atomic_helper_set_config+0x80/0x90 [drm_kms_helper]
? drm_mode_setcrtc+0x18d/0x690 [drm]
? tty_insert_flip_string_fixed_flag+0x85/0xe0
? drm_mode_getcrtc+0x180/0x180 [drm]
? drm_ioctl_kernel+0xb2/0xf0 [drm]
? drm_ioctl+0x25f/0x3f0 [drm]
? drm_mode_getcrtc+0x180/0x180 [drm]
? do_vfs_ioctl+0xa4/0x630
? ksys_ioctl+0x60/0x90
? ksys_write+0x4f/0xb0
? __x64_sys_ioctl+0x16/0x20
? do_syscall_64+0x5b/0x170
? entry_SYSCALL_64_after_hwframe+0x44/0xa9
This commit adds an entry to atomic_disable in the drm_crtc_helper_funcs
to avoid the NULL pointer dereference.
Fixes: 0f0eb98e33c6 ("drm/bochs: atomic: add atomic_flush+atomic_enable callbacks")
Signed-off-by: Rodrigo Siqueira <[email protected]>
---
drivers/gpu/drm/bochs/bochs_kms.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/gpu/drm/bochs/bochs_kms.c b/drivers/gpu/drm/bochs/bochs_kms.c
index 9e7cd6b34106..7e821776727f 100644
--- a/drivers/gpu/drm/bochs/bochs_kms.c
+++ b/drivers/gpu/drm/bochs/bochs_kms.c
@@ -35,6 +35,11 @@ static void bochs_crtc_atomic_enable(struct drm_crtc *crtc,
{
}
+static void bochs_crtc_atomic_disable(struct drm_crtc *crtc,
+ struct drm_crtc_state *old_state)
+{
+}
+
static void bochs_crtc_atomic_flush(struct drm_crtc *crtc,
struct drm_crtc_state *old_crtc_state)
{
@@ -66,6 +71,7 @@ static const struct drm_crtc_funcs bochs_crtc_funcs = {
static const struct drm_crtc_helper_funcs bochs_helper_funcs = {
.mode_set_nofb = bochs_crtc_mode_set_nofb,
.atomic_enable = bochs_crtc_atomic_enable,
+ .atomic_disable = bochs_crtc_atomic_disable,
.atomic_flush = bochs_crtc_atomic_flush,
};
--
2.21.0
On Sun, Mar 10, 2019 at 06:21:50PM -0300, Rodrigo Siqueira wrote:
> When the subtest basic-plain-flip from IGT project was executed on Bochs
> driver, the following bug appears:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
> ? drm_atomic_helper_commit_modeset_disables+0x396/0x3e0 [drm_kms_helper]
> +static void bochs_crtc_atomic_disable(struct drm_crtc *crtc,
> + struct drm_crtc_state *old_state)
> +{
> +}
> +
> static void bochs_crtc_atomic_flush(struct drm_crtc *crtc,
> struct drm_crtc_state *old_crtc_state)
> {
> @@ -66,6 +71,7 @@ static const struct drm_crtc_funcs bochs_crtc_funcs = {
> static const struct drm_crtc_helper_funcs bochs_helper_funcs = {
> .mode_set_nofb = bochs_crtc_mode_set_nofb,
> .atomic_enable = bochs_crtc_atomic_enable,
> + .atomic_disable = bochs_crtc_atomic_disable,
Shouldn't we make the callback optional instead of adding empty dummy
functions to drivers?
cheers,
Gerd
On 03/11, Gerd Hoffmann wrote:
> On Sun, Mar 10, 2019 at 06:21:50PM -0300, Rodrigo Siqueira wrote:
> > When the subtest basic-plain-flip from IGT project was executed on Bochs
> > driver, the following bug appears:
> >
> > BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
>
> > ? drm_atomic_helper_commit_modeset_disables+0x396/0x3e0 [drm_kms_helper]
>
> > +static void bochs_crtc_atomic_disable(struct drm_crtc *crtc,
> > + struct drm_crtc_state *old_state)
> > +{
> > +}
> > +
> > static void bochs_crtc_atomic_flush(struct drm_crtc *crtc,
> > struct drm_crtc_state *old_crtc_state)
> > {
> > @@ -66,6 +71,7 @@ static const struct drm_crtc_funcs bochs_crtc_funcs = {
> > static const struct drm_crtc_helper_funcs bochs_helper_funcs = {
> > .mode_set_nofb = bochs_crtc_mode_set_nofb,
> > .atomic_enable = bochs_crtc_atomic_enable,
> > + .atomic_disable = bochs_crtc_atomic_disable,
>
> Shouldn't we make the callback optional instead of adding empty dummy
> functions to drivers?
Hi Gerd,
I agree, and I can work in this issue.
Just one question, should we make atomic_enable optional as well?
Thanks for your feedback,
Best Regards
> cheers,
> Gerd
>
--
Rodrigo Siqueira
https://siqueira.tech
Graduate Student
Department of Computer Science
University of S?o Paulo
Hi,
> > > static void bochs_crtc_atomic_flush(struct drm_crtc *crtc,
> > > struct drm_crtc_state *old_crtc_state)
> > > {
> > > @@ -66,6 +71,7 @@ static const struct drm_crtc_funcs bochs_crtc_funcs = {
> > > static const struct drm_crtc_helper_funcs bochs_helper_funcs = {
> > > .mode_set_nofb = bochs_crtc_mode_set_nofb,
> > > .atomic_enable = bochs_crtc_atomic_enable,
> > > + .atomic_disable = bochs_crtc_atomic_disable,
> >
> > Shouldn't we make the callback optional instead of adding empty dummy
> > functions to drivers?
>
> Hi Gerd,
>
> I agree, and I can work in this issue.
> Just one question, should we make atomic_enable optional as well?
IIRC the drm code checks for the atomic_enable callback presence to
figure whenever it should take the atomic or legacy code paths.
So, I think that will not work.
cheers,
Gerd
On Mon, Mar 11, 2019 at 02:07:16PM +0100, Gerd Hoffmann wrote:
> Hi,
>
> > > > static void bochs_crtc_atomic_flush(struct drm_crtc *crtc,
> > > > struct drm_crtc_state *old_crtc_state)
> > > > {
> > > > @@ -66,6 +71,7 @@ static const struct drm_crtc_funcs bochs_crtc_funcs = {
> > > > static const struct drm_crtc_helper_funcs bochs_helper_funcs = {
> > > > .mode_set_nofb = bochs_crtc_mode_set_nofb,
> > > > .atomic_enable = bochs_crtc_atomic_enable,
> > > > + .atomic_disable = bochs_crtc_atomic_disable,
> > >
> > > Shouldn't we make the callback optional instead of adding empty dummy
> > > functions to drivers?
> >
> > Hi Gerd,
> >
> > I agree, and I can work in this issue.
> > Just one question, should we make atomic_enable optional as well?
>
> IIRC the drm code checks for the atomic_enable callback presence to
> figure whenever it should take the atomic or legacy code paths.
It should check for drm_driver->mode_config.funcs.atomic_commit for that,
see drm_drv_uses_atomic_modeset(). Anything else should be a bug.
Or do you mean the fallback to the old crtc helper prepare/commit
callbacks? We'd need to make all of them optional ofc, with atomic_
variants being preferred ofc.
-Daniel
>
> So, I think that will not work.
>
> cheers,
> Gerd
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
Hi,
> > IIRC the drm code checks for the atomic_enable callback presence to
> > figure whenever it should take the atomic or legacy code paths.
>
> It should check for drm_driver->mode_config.funcs.atomic_commit for that,
> see drm_drv_uses_atomic_modeset(). Anything else should be a bug.
>
> Or do you mean the fallback to the old crtc helper prepare/commit
> callbacks?
Probably the later. There was some reason why I've left in the empty
bochs_crtc_atomic_enable() callback ...
cheers,
Gerd
On 03/11, Gerd Hoffmann wrote:
> Hi,
>
> > > IIRC the drm code checks for the atomic_enable callback presence to
> > > figure whenever it should take the atomic or legacy code paths.
> >
> > It should check for drm_driver->mode_config.funcs.atomic_commit for that,
> > see drm_drv_uses_atomic_modeset(). Anything else should be a bug.
> >
> > Or do you mean the fallback to the old crtc helper prepare/commit
> > callbacks?
>
> Probably the later. There was some reason why I've left in the empty
> bochs_crtc_atomic_enable() callback ...
Just for checking before I start to work in this patch:
The correct solution should be made atomic_enable and atomic_disable
optional, right? I should do it, and check if Bochs driver really needs
bochs_crtc_atomic_enable after my change, right?
> cheers,
> Gerd
>
--
Rodrigo Siqueira
https://siqueira.tech
Graduate Student
Department of Computer Science
University of S?o Paulo
On Mon, Mar 11, 2019 at 02:49:58PM -0300, Rodrigo Siqueira wrote:
> On 03/11, Gerd Hoffmann wrote:
> > Hi,
> >
> > > > IIRC the drm code checks for the atomic_enable callback presence to
> > > > figure whenever it should take the atomic or legacy code paths.
> > >
> > > It should check for drm_driver->mode_config.funcs.atomic_commit for that,
> > > see drm_drv_uses_atomic_modeset(). Anything else should be a bug.
> > >
> > > Or do you mean the fallback to the old crtc helper prepare/commit
> > > callbacks?
> >
> > Probably the later. There was some reason why I've left in the empty
> > bochs_crtc_atomic_enable() callback ...
>
> Just for checking before I start to work in this patch:
> The correct solution should be made atomic_enable and atomic_disable
> optional, right? I should do it, and check if Bochs driver really needs
> bochs_crtc_atomic_enable after my change, right?
Yup. I just tried to remember why we haven't done this yet, but I think
that was a patch to make crtc->helper_funcs optional. And that doesn't
make sense imo, since if your crtc doesn't do anything then you don't
really have an atomic driver :-) And if there's ever a legit use case for
this, then that drive probably shouldn't use the atomic helpers ...
But making crtc_helper_funcs->atomic_enable/disable optional sounds like a
good idea.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch