[PATCH] drm/modes: Prevent division by zero htotal

Thu Jan 24 07:11:53 UTC 2019

> -----Original Message-----
> From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of Daniel Vetter
> Sent: Wednesday, January 23, 2019 6:56 PM
> To: Zhang, Tina <tina.zhang at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; dri-devel at lists.freedesktop.org; Adam
> Jackson <ajax at redhat.com>; Dave Airlie <airlied at redhat.com>; Daniel Vetter
> <daniel at ffwll.ch>
> Subject: Re: [PATCH] drm/modes: Prevent division by zero htotal
> 
> On Wed, Jan 23, 2019 at 03:28:59PM +0800, Tina Zhang wrote:
> > This patch prevents division by zero htotal.
> 
> How did you manage to get here with htotal == 0? This needs backtraces (or if
> this is just about static checkers, a mention of that).
> -Daniel

In GVT-g, we are trying to enable a virtual display w/o setting timings for a pipe
(a.k.a htotal=0), then we met the following kernel panic:

[   32.832048] divide error: 0000 [#1] SMP PTI
[   32.833614] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-rc4-sriov+ #33
[   32.834438] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.10.1-0-g8891697-dirty-20180511_165818-tinazhang-linux-1 04/01/2014
[   32.835901] RIP: 0010:drm_mode_hsync+0x1e/0x40
[   32.836004] Code: 31 c0 c3 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 8b 87 d8 00 00 00 85 c0 75 22 8b 4f 68 85 c9 78 1b 69 47 58 e8 03 00 00 99 <f7> f9 b9 d3 4d 62 10 05 f4 01 00 00 f7 e1 89 d0 c1 e8 06 f3 c3 66
[   32.836004] RSP: 0000:ffffc900000ebb90 EFLAGS: 00010206
[   32.836004] RAX: 0000000000000000 RBX: ffff88001c67c8a0 RCX: 0000000000000000
[   32.836004] RDX: 0000000000000000 RSI: ffff88001c67c000 RDI: ffff88001c67c8a0
[   32.836004] RBP: ffff88001c7d03a0 R08: ffff88001c67c8a0 R09: ffff88001c7d0330
[   32.836004] R10: ffffffff822c3a98 R11: 0000000000000001 R12: ffff88001c67c000
[   32.836004] R13: ffff88001c7d0370 R14: ffffffff8207eb78 R15: ffff88001c67c800
[   32.836004] FS:  0000000000000000(0000) GS:ffff88001da00000(0000) knlGS:0000000000000000
[   32.836004] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   32.836004] CR2: 0000000000000000 CR3: 000000000220a000 CR4: 00000000000006f0
[   32.836004] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   32.836004] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   32.836004] Call Trace:
[   32.836004]  intel_mode_from_pipe_config+0x72/0x90
[   32.836004]  intel_modeset_setup_hw_state+0x569/0xf90
[   32.836004]  intel_modeset_init+0x905/0x1db0
[   32.836004]  i915_driver_load+0xb8c/0x1120
[   32.836004]  i915_pci_probe+0x4d/0xb0
[   32.836004]  local_pci_probe+0x44/0xa0
[   32.836004]  ? pci_assign_irq+0x27/0x130
[   32.836004]  pci_device_probe+0x102/0x1c0
[   32.836004]  driver_probe_device+0x2b8/0x480
[   32.836004]  __driver_attach+0x109/0x110
[   32.836004]  ? driver_probe_device+0x480/0x480
[   32.836004]  bus_for_each_dev+0x67/0xc0
[   32.836004]  ? klist_add_tail+0x3b/0x70
[   32.836004]  bus_add_driver+0x1e8/0x260
[   32.836004]  driver_register+0x5b/0xe0
[   32.836004]  ? mipi_dsi_bus_init+0x11/0x11
[   32.836004]  do_one_initcall+0x4d/0x1eb
[   32.836004]  kernel_init_freeable+0x197/0x237
[   32.836004]  ? rest_init+0xd0/0xd0
[   32.836004]  kernel_init+0xa/0x110
[   32.836004]  ret_from_fork+0x35/0x40
[   32.836004] Modules linked in:
[   32.859183] ---[ end trace 525608b0ed0e8665 ]---
[   32.859722] RIP: 0010:drm_mode_hsync+0x1e/0x40
[   32.860287] Code: 31 c0 c3 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 8b 87 d8 00 00 00 85 c0 75 22 8b 4f 68 85 c9 78 1b 69 47 58 e8 03 00 00 99 <f7> f9 b9 d3 4d 62 10 05 f4 01 00 00 f7 e1 89 d0 c1 e8 06 f3 c3 66
[   32.862680] RSP: 0000:ffffc900000ebb90 EFLAGS: 00010206
[   32.863309] RAX: 0000000000000000 RBX: ffff88001c67c8a0 RCX: 0000000000000000
[   32.864182] RDX: 0000000000000000 RSI: ffff88001c67c000 RDI: ffff88001c67c8a0
[   32.865206] RBP: ffff88001c7d03a0 R08: ffff88001c67c8a0 R09: ffff88001c7d0330
[   32.866359] R10: ffffffff822c3a98 R11: 0000000000000001 R12: ffff88001c67c000
[   32.867213] R13: ffff88001c7d0370 R14: ffffffff8207eb78 R15: ffff88001c67c800
[   32.868075] FS:  0000000000000000(0000) GS:ffff88001da00000(0000) knlGS:0000000000000000
[   32.868983] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   32.869659] CR2: 0000000000000000 CR3: 000000000220a000 CR4: 00000000000006f0
[   32.870599] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   32.871598] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   32.872549] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Since drm_mode_hsync() has the logic to check mode->htotal, I just extend it to cover the case htotal==0.

Thanks.

BR,
Tina
> 
> >
> > Signed-off-by: Tina Zhang <tina.zhang at intel.com>
> > Cc: Adam Jackson <ajax at redhat.com>
> > Cc: Dave Airlie <airlied at redhat.com>
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > ---
> >  drivers/gpu/drm/drm_modes.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> > index adce9a2..59b92b1 100644
> > --- a/drivers/gpu/drm/drm_modes.c
> > +++ b/drivers/gpu/drm/drm_modes.c
> > @@ -751,7 +751,7 @@ int drm_mode_hsync(const struct
> drm_display_mode *mode)
> >  	if (mode->hsync)
> >  		return mode->hsync;
> >
> > -	if (mode->htotal < 0)
> > +	if (mode->htotal <= 0)
> >  		return 0;
> >
> >  	calc_val = (mode->clock * 1000) / mode->htotal; /* hsync in Hz */
> > --
> > 2.7.4
> >
> 
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch