| Message ID | 20190310212150.xhhb4abzm7j3ain2@smtp.gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/bochs: Fix NULL dereference on atomic_disable helper | expand |
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 >
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 >
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 >
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
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, };
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 <rodrigosiqueiramelo@gmail.com> --- drivers/gpu/drm/bochs/bochs_kms.c | 6 ++++++ 1 file changed, 6 insertions(+)