RE: [REGRESSION] Divide-by-zero on DisplayPort MST unplug with nouveau

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> -----Original Message-----
> From: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Sent: Monday, 11 March 2024 18.03
> To: Saarinen, Jani <jani.saarinen@xxxxxxxxx>; Linux regressions mailing list
> <regressions@xxxxxxxxxxxxxxx>; Deak, Imre <imre.deak@xxxxxxxxx>
> Cc: Chris Bainbridge <chris.bainbridge@xxxxxxxxx>; intel-gfx <intel-
> gfx@xxxxxxxxxxxxxxxxxxxxx>; David Airlie <airlied@xxxxxxxx>; Daniel Vetter
> <daniel@xxxxxxxx>; ML dri-devel <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
> Subject: RE: [REGRESSION] Divide-by-zero on DisplayPort MST unplug with
> nouveau
> 
> On Mon, 11 Mar 2024, "Saarinen, Jani" <jani.saarinen@xxxxxxxxx> wrote:
> > Hi,
> >
> >> -----Original Message-----
> >> From: Intel-gfx <intel-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf
> >> Of Linux regression tracking (Thorsten Leemhuis)
> >> Sent: Monday, 11 March 2024 17.53
> >> To: Deak, Imre <imre.deak@xxxxxxxxx>
> >> Cc: regressions@xxxxxxxxxxxxxxx; Chris Bainbridge
> >> <chris.bainbridge@xxxxxxxxx>; intel-gfx
> >> <intel-gfx@xxxxxxxxxxxxxxxxxxxxx>;
> >> David Airlie <airlied@xxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx>; ML
> >> dri-devel <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
> >> Subject: Re: [REGRESSION] Divide-by-zero on DisplayPort MST unplug
> >> with nouveau
> >>
> >> On 07.03.24 18:58, Chris Bainbridge wrote:
> >> > ----- Forwarded message from Chris Bainbridge
> >> > <chris.bainbridge@xxxxxxxxx> -----
> >> >
> >> > Date: Sat, 10 Feb 2024 21:24:59 +0000
> >>
> >> Hmm, it looks like nobody is looking into this regression. Is there a
> >> good reason?
> >>
> >> Imre, or did you maybe just miss that Chris' regression seems to be
> >> caused by a commit of yours? He initally proposed a fix (the
> >> forwarded mail that is quoted here) more a month ago already here:
> >> https://lore.kernel.org/all/ZcfpqwnkSoiJxeT9@debian.local/
> >>
> >> Chris recently filed a ticket, too:
> >> https://gitlab.freedesktop.org/drm/misc/kernel/-/issues/36
> > Please file
> > https://drm.pages.freedesktop.org/intel-docs/how-to-file-i915-bugs.htm
> > l
> 
> Well, please don't. It's *not* an i915 bug.
Right, sorry about this. Let Imre to comment then. 

> 
> BR,
> Jani.
> 
> >>
> >> Mostly silence there as well. :-/
> >>
> >> Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker'
> >> hat)
> >>
> >> P.S: Chris, sorry, I had missed that you initially proposed the fix a
> >> month ago; if I had noticed this earlier I had sent a mail like this one earlier.
> >> --
> >> Everything you wanna know about Linux kernel regression tracking:
> >> https://linux-regtracking.leemhuis.info/about/#tldr
> >> If I did something stupid, please tell me, as explained on that page.
> >>
> >> > From: Chris Bainbridge <chris.bainbridge@xxxxxxxxx>
> >> > To: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> >> > Cc: lyude@xxxxxxxxxx, ville.syrjala@xxxxxxxxxxxxxxx,
> >> stanislav.lisovskiy@xxxxxxxxx,
> >> > 	mripard@xxxxxxxxxx, imre.deak@xxxxxxxxx
> >> > Subject: [PATCH] Fix divide-by-zero on DP unplug with nouveau
> >> >
> >> > The following trace occurs when using nouveau and unplugging a DP
> >> > MST
> >> > adaptor:
> >> >>  divide error: 0000 [#1] PREEMPT SMP PTI
> >> >  CPU: 7 PID: 2962 Comm: Xorg Not tainted 6.8.0-rc3+ #744  Hardware
> >> > name: Razer Blade/DANA_MB, BIOS 01.01 08/31/2018
> >> >  RIP: 0010:drm_dp_bw_overhead+0xb4/0x110 [drm_display_helper]
> >> >  Code: c6 b8 01 00 00 00 75 61 01 c6 41 0f af f3 41 0f af f1 c1 e1
> >> > 04
> >> > 48 63 c7 31 d2 89 ff 48 8b 5d f8 c9 48 0f af f1 48 8d 44 06 ff <48>
> >> > f7
> >> > f7 31 d2 31 c9 31 f6 31 ff 45 31 c0 45 31 c9 45 31 d2 45 31
> >> >  RSP: 0018:ffffb2c5c211fa30 EFLAGS: 00010206
> >> >  RAX: ffffffffffffffff RBX: 0000000000000000 RCX: 0000000000f59b00
> >> >  RDX: 0000000000000000 RSI: 0000000000000000 RDI:
> >> 0000000000000000
> >> >  RBP: ffffb2c5c211fa48 R08: 0000000000000001 R09:
> >> 0000000000000020
> >> >  R10: 0000000000000004 R11: 0000000000000000 R12:
> >> 0000000000023b4a
> >> >  R13: ffff91d37d165800 R14: ffff91d36fac6d80 R15: ffff91d34a764010
> >> >  FS:  00007f4a1ca3fa80(0000) GS:ffff91d6edbc0000(0000)
> >> > knlGS:0000000000000000
> >> >  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> >  CR2: 0000559491d49000 CR3: 000000011d180002 CR4:
> >> 00000000003706f0
> >> > Call Trace:
> >> >   <TASK>
> >> >   ? show_regs+0x6d/0x80
> >> >   ? die+0x37/0xa0
> >> >   ? do_trap+0xd4/0xf0
> >> >   ? do_error_trap+0x71/0xb0
> >> >   ? drm_dp_bw_overhead+0xb4/0x110 [drm_display_helper]
> >> >   ? exc_divide_error+0x3a/0x70
> >> >   ? drm_dp_bw_overhead+0xb4/0x110 [drm_display_helper]
> >> >   ? asm_exc_divide_error+0x1b/0x20
> >> >   ? drm_dp_bw_overhead+0xb4/0x110 [drm_display_helper]
> >> >   ? drm_dp_calc_pbn_mode+0x2e/0x70 [drm_display_helper]
> >> >   nv50_msto_atomic_check+0xda/0x120 [nouveau]
> >> >   drm_atomic_helper_check_modeset+0xa87/0xdf0 [drm_kms_helper]
> >> >   drm_atomic_helper_check+0x19/0xa0 [drm_kms_helper]
> >> >   nv50_disp_atomic_check+0x13f/0x2f0 [nouveau]
> >> >   drm_atomic_check_only+0x668/0xb20 [drm]
> >> >   ? drm_connector_list_iter_next+0x86/0xc0 [drm]
> >> >   drm_atomic_commit+0x58/0xd0 [drm]
> >> >   ? __pfx___drm_printfn_info+0x10/0x10 [drm]
> >> >   drm_atomic_connector_commit_dpms+0xd7/0x100 [drm]
> >> >   drm_mode_obj_set_property_ioctl+0x1c5/0x450 [drm]
> >> >   ? __pfx_drm_connector_property_set_ioctl+0x10/0x10 [drm]
> >> >   drm_connector_property_set_ioctl+0x3b/0x60 [drm]
> >> >   drm_ioctl_kernel+0xb9/0x120 [drm]
> >> >   drm_ioctl+0x2d0/0x550 [drm]
> >> >   ? __pfx_drm_connector_property_set_ioctl+0x10/0x10 [drm]
> >> >   nouveau_drm_ioctl+0x61/0xc0 [nouveau]
> >> >   __x64_sys_ioctl+0xa0/0xf0
> >> >   do_syscall_64+0x76/0x140
> >> >   ? do_syscall_64+0x85/0x140
> >> >   ? do_syscall_64+0x85/0x140
> >> >   entry_SYSCALL_64_after_hwframe+0x6e/0x76
> >> >  RIP: 0033:0x7f4a1cd1a94f
> >> >  Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00
> >> > 48
> >> > 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <41>
> >> > 89
> >> > c0 3d 00 f0 ff ff 77 1f 48 8b 44 24 18 64 48 2b 04 25 28 00
> >> >  RSP: 002b:00007ffd2f1df520 EFLAGS: 00000246 ORIG_RAX:
> >> > 0000000000000010
> >> >  RAX: ffffffffffffffda RBX: 00007ffd2f1df5b0 RCX: 00007f4a1cd1a94f
> >> >  RDX: 00007ffd2f1df5b0 RSI: 00000000c01064ab RDI:
> 000000000000000f
> >> >  RBP: 00000000c01064ab R08: 000056347932deb8 R09:
> >> 000056347a7d99c0
> >> >  R10: 0000000000000000 R11: 0000000000000246 R12:
> >> 000056347938a220
> >> >  R13: 000000000000000f R14: 0000563479d9f3f0 R15:
> >> 0000000000000000
> >> >   </TASK>
> >> >  Modules linked in: rfcomm xt_conntrack nft_chain_nat xt_MASQUERADE
> >> nf_nat nf_conntrack_netlink nf_conntrack nf_defrag_ipv6
> >> nf_defrag_ipv4 xfrm_user xfrm_algo xt_addrtype nft_compat nf_tables
> >> nfnetlink br_netfilter bridge stp llc ccm cmac algif_hash overlay
> >> algif_skcipher af_alg bnep binfmt_misc snd_sof_pci_intel_cnl
> >> snd_sof_intel_hda_common snd_soc_hdac_hda snd_sof_pci
> >> snd_sof_xtensa_dsp snd_sof_intel_hda snd_sof snd_sof_utils
> >> snd_soc_acpi_intel_match snd_soc_acpi snd_soc_core snd_compress
> >> snd_sof_intel_hda_mlink snd_hda_ext_core iwlmvm intel_rapl_msr
> >> intel_rapl_common intel_tcc_cooling x86_pkg_temp_thermal
> >> intel_powerclamp mac80211 coretemp kvm_intel snd_hda_codec_hdmi
> kvm
> >> snd_hda_codec_realtek snd_hda_codec_generic uvcvideo libarc4
> >> snd_hda_intel snd_intel_dspcfg snd_hda_codec iwlwifi
> >> videobuf2_vmalloc videobuf2_memops uvc irqbypass btusb
> videobuf2_v4l2
> >> snd_seq_midi crct10dif_pclmul hid_multitouch crc32_pclmul
> >> snd_seq_midi_event btrtl snd_hwdep videodev polyval_clmulni
> >> polyval_generic snd_rawmidi
> >> >   ghash_clmulni_intel aesni_intel btintel crypto_simd snd_hda_core
> >> > cryptd snd_seq btbcm ee1004 8250_dw videobuf2_common btmtk rapl
> >> > nls_iso8859_1 mei_hdcp thunderbolt bluetooth intel_cstate wmi_bmof
> >> > intel_wmi_thunderbolt cfg80211 snd_pcm mc snd_seq_device i2c_i801
> >> > r8169 ecdh_generic snd_timer i2c_smbus ecc snd mei_me
> >> > intel_lpss_pci mei ahci intel_lpss soundcore realtek libahci idma64
> >> > intel_pch_thermal i2c_hid_acpi i2c_hid acpi_pad sch_fq_codel msr
> >> > parport_pc ppdev lp parport efi_pstore ip_tables x_tables autofs4
> >> > dm_crypt raid10 raid456 libcrc32c async_raid6_recov async_memcpy
> >> > async_pq async_xor xor async_tx raid6_pq raid1 raid0 joydev
> >> > input_leds hid_generic usbhid hid nouveau i915 drm_ttm_helper
> >> > gpu_sched drm_gpuvm drm_exec
> >> i2c_algo_bit
> >> > drm_buddy ttm drm_display_helper drm_kms_helper cec rc_core drm
> >> > nvme nvme_core mxm_wmi xhci_pci xhci_pci_renesas video wmi
> >> > pinctrl_cannonlake mac_hid  ---[ end trace 0000000000000000 ]---
> >> >
> >> > Fix this by avoiding the divide if bpp is 0.
> >> >
> >> > Fixes: c1d6a22b7219 ("drm/dp: Add helpers to calculate the link BW
> >> > overhead")
> >> > Signed-off-by: Chris Bainbridge <chris.bainbridge@xxxxxxxxx>
> >> > ---
> >> >  drivers/gpu/drm/display/drm_dp_helper.c | 3 +++
> >> >  1 file changed, 3 insertions(+)
> >> >
> >> > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c
> >> > b/drivers/gpu/drm/display/drm_dp_helper.c
> >> > index b1ca3a1100da..bb8794c8f99c 100644
> >> > --- a/drivers/gpu/drm/display/drm_dp_helper.c
> >> > +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> >> > @@ -4024,6 +4024,9 @@ int drm_dp_bw_overhead(int lane_count, int
> >> hactive,
> >> >  							  bpp_x16,
> >> symbol_size,
> >> >  							  is_mst);
> >> >
> >> > +	/* Avoid potential divide by zero in DIV_ROUND_UP_ULL */
> >> > +	if (bpp_x16 == 0)
> >> > +		return 0;
> >> >  	return DIV_ROUND_UP_ULL(mul_u32_u32(symbol_cycles *
> >> symbol_size * lane_count,
> >> >  					    overhead * 16),
> >> >  				hactive * bpp_x16);
> >>
> >> P. P.S.:
> >>
> >> #regzbot duplicate:
> >> https://lore.kernel.org/all/ZcfpqwnkSoiJxeT9@debian.local/
> >> #regzbot poke
> 
> --
> Jani Nikula, Intel




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