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Date:   Mon, 3 Apr 2023 09:25:41 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Rob Clark <robdclark@gmail.com>
Cc:     dri-devel@lists.freedesktop.org,
        Rob Clark <robdclark@chromium.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] drm/vblank: Fix for drivers that do not
 drm_vblank_init()
Message-ID: <20230403162541.GA3195909@dev-arch.thelio-3990X>
References: <20230403160314.1210533-1-robdclark@gmail.com>
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In-Reply-To: <20230403160314.1210533-1-robdclark@gmail.com>
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On Mon, Apr 03, 2023 at 09:03:14AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> This should fix a crash that was reported on ast (and possibly other
> drivers which do not initialize vblank).
> 
>    fbcon: Taking over console
>    Unable to handle kernel NULL pointer dereference at virtual address 0000000000000074
>    Mem abort info:
>      ESR = 0x0000000096000004
>      EC = 0x25: DABT (current EL), IL = 32 bits
>      SET = 0, FnV = 0
>      EA = 0, S1PTW = 0
>      FSC = 0x04: level 0 translation fault
>    Data abort info:
>      ISV = 0, ISS = 0x00000004
>      CM = 0, WnR = 0
>    user pgtable: 4k pages, 48-bit VAs, pgdp=0000080009d16000
>    [0000000000000074] pgd=0000000000000000, p4d=0000000000000000
>    Internal error: Oops: 0000000096000004 [#1] SMP
>    Modules linked in: ip6table_nat tun nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nf_tables nfnetlink qrtr sunrpc binfmt_misc vfat fat xfs snd_usb_audio snd_hwdep snd_usbmidi_lib snd_seq snd_pcm snd_rawmidi snd_timer snd_seq_device snd soundcore joydev mc ipmi_ssif ipmi_devintf ipmi_msghandler arm_spe_pmu arm_cmn arm_dsu_pmu arm_dmc620_pmu cppc_cpufreq loop zram crct10dif_ce polyval_ce nvme polyval_generic ghash_ce sbsa_gwdt igb nvme_core ast nvme_common i2c_algo_bit xgene_hwmon gpio_dwapb scsi_dh_rdac scsi_dh_emc scsi_dh_alua ip6_tables ip_tables dm_multipath fuse
>    CPU: 12 PID: 469 Comm: kworker/12:1 Not tainted 6.3.0-rc2-00008-gd39e48ca80c0 #1
>    Hardware name: ADLINK AVA Developer Platform/AVA Developer Platform, BIOS TianoCore 2.04.100.07 (SYS: 2.06.20220308) 09/08/2022
>    Workqueue: events fbcon_register_existing_fbs
>    pstate: 20400009 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>    pc : drm_crtc_next_vblank_start+0x2c/0x98
>    lr : drm_atomic_helper_wait_for_fences+0x90/0x240
>    sp : ffff80000d583960
>    x29: ffff80000d583960 x28: ffff07ff8fc187b0 x27: 0000000000000000
>    x26: ffff07ff99c08c00 x25: 0000000000000038 x24: ffff07ff99c0c000
>    x23: 0000000000000001 x22: 0000000000000038 x21: 0000000000000000
>    x20: ffff07ff9640a280 x19: 0000000000000000 x18: ffffffffffffffff
>    x17: 0000000000000000 x16: ffffb24d2eece1c0 x15: 0000003038303178
>    x14: 3032393100000048 x13: 0000000000000000 x12: 0000000000000000
>    x11: 0000000000000000 x10: 0000000000000000 x9 : ffffb24d2eeeaca0
>    x8 : ffff80000d583628 x7 : 0000080077783000 x6 : 0000000000000000
>    x5 : ffff80000d584000 x4 : ffff07ff99c0c000 x3 : 0000000000000130
>    x2 : 0000000000000000 x1 : ffff80000d5839c0 x0 : ffff07ff99c0cc08
>    Call trace:
>     drm_crtc_next_vblank_start+0x2c/0x98
>     drm_atomic_helper_wait_for_fences+0x90/0x240
>     drm_atomic_helper_commit+0xb0/0x188
>     drm_atomic_commit+0xb0/0xf0
>     drm_client_modeset_commit_atomic+0x218/0x280
>     drm_client_modeset_commit_locked+0x64/0x1a0
>     drm_client_modeset_commit+0x38/0x68
>     __drm_fb_helper_restore_fbdev_mode_unlocked+0xb0/0xf8
>     drm_fb_helper_set_par+0x44/0x88
>     fbcon_init+0x1e0/0x4a8
>     visual_init+0xbc/0x118
>     do_bind_con_driver.isra.0+0x194/0x3a0
>     do_take_over_console+0x50/0x70
>     do_fbcon_takeover+0x74/0xf8
>     do_fb_registered+0x13c/0x158
>     fbcon_register_existing_fbs+0x78/0xc0
>     process_one_work+0x1ec/0x478
>     worker_thread+0x74/0x418
>     kthread+0xec/0x100
>     ret_from_fork+0x10/0x20
>    Code: f9400004 b9409013 f940a082 9ba30a73 (b9407662)
>    ---[ end trace 0000000000000000 ]---
> 
> v2: Use drm_dev_has_vblank()
> 
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Fixes: d39e48ca80c0 ("drm/atomic-helper: Set fence deadline for vblank")
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

Still appears to work for me:

Tested-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  drivers/gpu/drm/drm_vblank.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 299fa2a19a90..877e2067534f 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -996,10 +996,16 @@ EXPORT_SYMBOL(drm_crtc_vblank_count_and_time);
>  int drm_crtc_next_vblank_start(struct drm_crtc *crtc, ktime_t *vblanktime)
>  {
>  	unsigned int pipe = drm_crtc_index(crtc);
> -	struct drm_vblank_crtc *vblank = &crtc->dev->vblank[pipe];
> -	struct drm_display_mode *mode = &vblank->hwmode;
> +	struct drm_vblank_crtc *vblank;
> +	struct drm_display_mode *mode;
>  	u64 vblank_start;
>  
> +	if (!drm_dev_has_vblank(crtc->dev))
> +		return -EINVAL;
> +
> +	vblank = &crtc->dev->vblank[pipe];
> +	mode = &vblank->hwmode;
> +
>  	if (!vblank->framedur_ns || !vblank->linedur_ns)
>  		return -EINVAL;
>  
> -- 
> 2.39.2
>