[PATCH] drm/atomic_helper: Add missing NULL check for drm_plane_helper_funcs.atomic_update
Something I discovered while writing rvkms since some versions of the driver didn't have a filled out atomic_update function - we mention that this callback is "optional", but we don't actually check whether it's NULL or not before calling it. As a result, we'll segfault if it's not filled in.
rvkms rvkms.0: [drm:drm_atomic_helper_commit_modeset_disables] modeset on [ENCODER:36:Virtual-36] BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0010 [#1] PREEMPT SMP NOPTI Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240813-1.fc40 08/13/2024 RIP: 0010:0x0
So, let's fix that.
Signed-off-by: Lyude Paul lyude@redhat.com Fixes: c2fcd274bce5 ("drm: Add atomic/plane helpers") Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v3.19+ --- drivers/gpu/drm/drm_atomic_helper.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 43cdf39019a44..b3c507040c6d6 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -2797,7 +2797,8 @@ void drm_atomic_helper_commit_planes(struct drm_device *dev,
funcs->atomic_disable(plane, old_state); } else if (new_plane_state->crtc || disabling) { - funcs->atomic_update(plane, old_state); + if (funcs->atomic_update) + funcs->atomic_update(plane, old_state);
if (!disabling && funcs->atomic_enable) { if (drm_atomic_plane_enabling(old_plane_state, new_plane_state)) @@ -2889,7 +2890,8 @@ drm_atomic_helper_commit_planes_on_crtc(struct drm_crtc_state *old_crtc_state) if (disabling && plane_funcs->atomic_disable) { plane_funcs->atomic_disable(plane, old_state); } else if (new_plane_state->crtc || disabling) { - plane_funcs->atomic_update(plane, old_state); + if (plane_funcs->atomic_update) + plane_funcs->atomic_update(plane, old_state);
if (!disabling && plane_funcs->atomic_enable) { if (drm_atomic_plane_enabling(old_plane_state, new_plane_state))
base-commit: 22512c3ee0f47faab5def71c4453638923c62522
Am 27.09.24 um 22:46 schrieb Lyude Paul:
Something I discovered while writing rvkms since some versions of the driver didn't have a filled out atomic_update function - we mention that this callback is "optional", but we don't actually check whether it's NULL or not before calling it. As a result, we'll segfault if it's not filled in.
rvkms rvkms.0: [drm:drm_atomic_helper_commit_modeset_disables] modeset on [ENCODER:36:Virtual-36] BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0010 [#1] PREEMPT SMP NOPTI Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240813-1.fc40 08/13/2024 RIP: 0010:0x0
So, let's fix that.
Signed-off-by: Lyude Paul lyude@redhat.com Fixes: c2fcd274bce5 ("drm: Add atomic/plane helpers") Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v3.19+
Reviewed-by: Thomas Zimmermann tzimmermann@suse.de
drivers/gpu/drm/drm_atomic_helper.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 43cdf39019a44..b3c507040c6d6 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -2797,7 +2797,8 @@ void drm_atomic_helper_commit_planes(struct drm_device *dev, funcs->atomic_disable(plane, old_state); } else if (new_plane_state->crtc || disabling) {
funcs->atomic_update(plane, old_state);
if (funcs->atomic_update)funcs->atomic_update(plane, old_state);if (!disabling && funcs->atomic_enable) { if (drm_atomic_plane_enabling(old_plane_state, new_plane_state)) @@ -2889,7 +2890,8 @@ drm_atomic_helper_commit_planes_on_crtc(struct drm_crtc_state *old_crtc_state) if (disabling && plane_funcs->atomic_disable) { plane_funcs->atomic_disable(plane, old_state); } else if (new_plane_state->crtc || disabling) {
plane_funcs->atomic_update(plane, old_state);
if (plane_funcs->atomic_update)plane_funcs->atomic_update(plane, old_state);if (!disabling && plane_funcs->atomic_enable) { if (drm_atomic_plane_enabling(old_plane_state, new_plane_state))
base-commit: 22512c3ee0f47faab5def71c4453638923c62522
Hi,
On Fri, Sep 27, 2024 at 04:46:16PM GMT, Lyude Paul wrote:
Something I discovered while writing rvkms since some versions of the driver didn't have a filled out atomic_update function - we mention that this callback is "optional", but we don't actually check whether it's NULL or not before calling it. As a result, we'll segfault if it's not filled in.
rvkms rvkms.0: [drm:drm_atomic_helper_commit_modeset_disables] modeset on [ENCODER:36:Virtual-36] BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0010 [#1] PREEMPT SMP NOPTI Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240813-1.fc40 08/13/2024 RIP: 0010:0x0
So, let's fix that.
Signed-off-by: Lyude Paul lyude@redhat.com Fixes: c2fcd274bce5 ("drm: Add atomic/plane helpers") Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v3.19+
So we had kind of a similar argument with drm_connector_init early this year, but I do agree we shouldn't fault if we're missing a callback.
I do wonder how we can implement a plane without atomic_update though? Do we have drivers in such a case?
If not, a better solution would be to make it mandatory and check it when registering.
Maxime
Hi
Am 30.09.24 um 09:01 schrieb Maxime Ripard:
Hi,
On Fri, Sep 27, 2024 at 04:46:16PM GMT, Lyude Paul wrote:
Something I discovered while writing rvkms since some versions of the driver didn't have a filled out atomic_update function - we mention that this callback is "optional", but we don't actually check whether it's NULL or not before calling it. As a result, we'll segfault if it's not filled in.
rvkms rvkms.0: [drm:drm_atomic_helper_commit_modeset_disables] modeset on [ENCODER:36:Virtual-36] BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0010 [#1] PREEMPT SMP NOPTI Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240813-1.fc40 08/13/2024 RIP: 0010:0x0
So, let's fix that.
Signed-off-by: Lyude Paul lyude@redhat.com Fixes: c2fcd274bce5 ("drm: Add atomic/plane helpers") Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v3.19+
So we had kind of a similar argument with drm_connector_init early this year, but I do agree we shouldn't fault if we're missing a callback.
I do wonder how we can implement a plane without atomic_update though? Do we have drivers in such a case?
That would likely be an output with an entirely static display. Hard to imaging, I think.
If not, a better solution would be to make it mandatory and check it when registering.
Although I r-b'ed the patch already, I'd also prefer this solution.
Maxime
On Mon, 2024-09-30 at 09:06 +0200, Thomas Zimmermann wrote:
Hi
Am 30.09.24 um 09:01 schrieb Maxime Ripard:
Hi,
On Fri, Sep 27, 2024 at 04:46:16PM GMT, Lyude Paul wrote:
Something I discovered while writing rvkms since some versions of the driver didn't have a filled out atomic_update function - we mention that this callback is "optional", but we don't actually check whether it's NULL or not before calling it. As a result, we'll segfault if it's not filled in.
rvkms rvkms.0: [drm:drm_atomic_helper_commit_modeset_disables] modeset on [ENCODER:36:Virtual-36] BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0010 [#1] PREEMPT SMP NOPTI Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240813-1.fc40 08/13/2024 RIP: 0010:0x0
So, let's fix that.
Signed-off-by: Lyude Paul lyude@redhat.com Fixes: c2fcd274bce5 ("drm: Add atomic/plane helpers") Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v3.19+
So we had kind of a similar argument with drm_connector_init early this year, but I do agree we shouldn't fault if we're missing a callback.
I do wonder how we can implement a plane without atomic_update though? Do we have drivers in such a case?
That would likely be an output with an entirely static display. Hard to imaging, I think.
If not, a better solution would be to make it mandatory and check it when registering.
Although I r-b'ed the patch already, I'd also prefer this solution.
Gotcha, FWIW the reason I went with this patch: * atomic_update is actually documented as being optional in the kernel docs, so we'd want to remove that if we make it mandatory * rvkms currently doesn't have an atomic_update. We will likely have one whenever I get a chance to actually add CRC and/or writeback connector supports - but for the time being all we do is register a KMS device with vblank support.
I am fine with either solution though
Maxime
Hi,
On Mon, Sep 30, 2024 at 03:45:13PM -0400, Lyude Paul wrote:
On Mon, 2024-09-30 at 09:06 +0200, Thomas Zimmermann wrote:
Hi
Am 30.09.24 um 09:01 schrieb Maxime Ripard:
Hi,
On Fri, Sep 27, 2024 at 04:46:16PM GMT, Lyude Paul wrote:
Something I discovered while writing rvkms since some versions of the driver didn't have a filled out atomic_update function - we mention that this callback is "optional", but we don't actually check whether it's NULL or not before calling it. As a result, we'll segfault if it's not filled in.
rvkms rvkms.0: [drm:drm_atomic_helper_commit_modeset_disables] modeset on [ENCODER:36:Virtual-36] BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0010 [#1] PREEMPT SMP NOPTI Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240813-1.fc40 08/13/2024 RIP: 0010:0x0
So, let's fix that.
Signed-off-by: Lyude Paul lyude@redhat.com Fixes: c2fcd274bce5 ("drm: Add atomic/plane helpers") Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v3.19+
So we had kind of a similar argument with drm_connector_init early this year, but I do agree we shouldn't fault if we're missing a callback.
I do wonder how we can implement a plane without atomic_update though? Do we have drivers in such a case?
That would likely be an output with an entirely static display. Hard to imaging, I think.
If not, a better solution would be to make it mandatory and check it when registering.
Although I r-b'ed the patch already, I'd also prefer this solution.
Gotcha, FWIW the reason I went with this patch:
- atomic_update is actually documented as being optional in the kernel docs, so we'd want to remove that if we make it mandatory
Sure, that makes total sense :)
- rvkms currently doesn't have an atomic_update. We will likely have one whenever I get a chance to actually add CRC and/or writeback connector supports - but for the time being all we do is register a KMS device with vblank support.
WIP drivers can provide an empty implementation. And even if actually didn't need it for $REASONS, I'd argue that an empty implementation (and a comment) makes that explicit instead of making the reader guess why it's not needed.
Maxime
linux-stable-mirror@lists.linaro.org
-
Lyude Paul -
Maxime Ripard -
Thomas Zimmermann