Date:   Wed, 20 Jun 2018 10:39:43 +0200
From:   Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:     Caicai <caizhaopeng@...pin.com>, gustavo@...ovan.org
Cc:     seanpaul@...omium.org, airlied@...ux.ie,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH] drm: fix pci_dev root device is NULL without check.

Op 19-06-18 om 09:47 schreef Caicai:
>     on my laptop with ATI Radeon R7 350 graphics card,I found root was NULL,we should check
>     the device before get/set pcie speed cap mask. Here is my messages.
>     [    8.996093] [drm] radeon kernel modesetting enabled.
>     [    8.996093] [drm] initializing kernel modesetting (OLAND 0x1002:0x6610 0x174B:0xA00B).
>     [    8.996093] [drm] register mmio base: 0x10000000
>     [    8.996093] [drm] register mmio size: 262144
>     [    9.121093] ATOM BIOS: C55001
>     [    9.121093] [drm] GPU not posted. posting now...
>     [    9.125000] radeon 0001:20:00.0: VRAM: 2048M 0x0000000000000000 - 0x000000007FFFFFFF (2048M used)
>     [    9.125000] radeon 0001:20:00.0: GTT: 2048M 0x0000000080000000 - 0x00000000FFFFFFFF
>     [    9.125000] [drm] Detected VRAM RAM=2048M, BAR=256M
>     [    9.125000] [drm] RAM width 128bits DDR
>     [    9.125000] [drm] radeon: 2048M of VRAM memory ready
>     [    9.125000] [drm] radeon: 2048M of GTT memory ready.
>     [    9.125000] [drm] Loading oland Microcode
>     [    9.128906] [drm] Internal thermal controller with fan control
>     [    9.128906] Unable to handle kernel paging request at virtual address 000000000000003c
>     [    9.128906] CPU 3 systemd-udevd(148): Oops 0
>     [    9.128906] pc = [<ffffffff80e63824>]  ra = [<fffffffc03faf914>]  ps = 0000    Not tainted
>     [    9.128906] pc is at drm_pcie_get_speed_cap_mask+0x3c/0x12c
>     [    9.128906] ra is at si_dpm_init+0x64/0x1398 [radeon]
>     [    9.128906] v0 = ffffffffffffffea  t0 = fffffc07fcc3a400  t1 = 0000000000001106
>     [    9.128906] t2 = 0000000000001166  t3 = 0000000000000000  t4 = fffffc018eafc000
>     [    9.128906] t5 = ffffffffffffff80  t6 = 000000000000003f  t7 = fffffc07f6a90000
>     [    9.128906] s0 = fffffc07f6a9390c  s1 = 0000000000000000  s2 = fffffc07f59119b0
>     [    9.128906] s3 = 0000000000000001  s4 = fffffffffffffff4  s5 = fffffc07f5910000
>     [    9.128906] s6 = 0000000000000000
>     [    9.128906] a0 = fffffc07f706c800  a1 = fffffc07f6a9390c  a2 = fffffffffffffffc
>     [    9.128906] a3 = ffffffff815fb510  a4 = ffffffff815fb4c8  a5 = 0000000000000000
>     [    9.128906] t8 = 000000000000007f  t9 = ffffffff80d86c14  t10= 0000000000000001
>     [    9.128906] t11= 00000000000003c0  pv = ffffffff80e637e8  at = 0000000000000000
>     [    9.128906] gp = ffffffff815e9230  sp = fffffc07f6a93868
>     [    9.128906] Disabling lock debugging due to kernel taint
>     [    9.128906] Trace:
>     [    9.128906] [<ffffffff80e61260>] drm_dev_register+0xb0/0x138
>     [    9.128906] [<ffffffff80e64368>] drm_get_pci_dev+0x120/0x208
>     [    9.128906] [<ffffffff80dcced4>] local_pci_probe+0x38/0x8c
>     [    9.128906] [<ffffffff80dcdac0>] pci_device_probe+0x170/0x1d0
>     [    9.128906] [<ffffffff80e9d654>] driver_probe_device+0x168/0x2fc
>     [    9.128906] [<ffffffff80e9d87c>] __driver_attach+0x94/0xe8
>     [    9.128906] [<ffffffff80e9acf4>] bus_for_each_dev+0x94/0xd4
>     [    9.128906] [<ffffffff80e9d7e8>] __driver_attach+0x0/0xe8
>     [    9.128906] [<ffffffff80e9ce98>] driver_attach+0x2c/0x40
>     [    9.128906] [<ffffffff80e9c870>] bus_add_driver+0x140/0x2d4
>     [    9.128906] [<ffffffff80e9e28c>] driver_register+0x100/0x180
>     [    9.128906] [<ffffffff80dccda0>] __pci_register_driver+0x48/0x5c
>     [    9.128906] [<ffffffff80e644cc>] drm_pci_init+0x7c/0x168
>     [    9.128906] [<ffffffff809102fc>] do_one_initcall+0x188/0x25c
>     [    9.128906] [<ffffffff809f5f00>] do_init_module+0x8c/0x2c8
>     [    9.128906] [<ffffffff80a5b698>] kmem_cache_alloc+0x1f8/0x22c
>     [    9.128906] [<ffffffff809f5eb4>] do_init_module+0x40/0x2c8
>     [    9.128906] [<ffffffff809b36c8>] load_module+0x1ea8/0x263c
>     [    9.128906] [<ffffffff809af9fc>] unknown_module_param_cb+0x0/0xc8
>     [    9.128906] [<ffffffff809b40a4>] SYSC_finit_module+0x94/0xb4
>     [    9.128906] [<ffffffff809aeb68>] module_notes_read+0x0/0x4c
>     [    9.128906] [<ffffffff80911040>] entSys+0xa0/0xc0
Grepping on entSys the only mention is on alpha.

Is dev->pdev->bus->parent NULL by any chance?
>     [    9.128906] Code: 8c300188  c020003b  8c210010  f85f1106  f87f1166  8d410038 <842a003c> 40220502
>     [    9.128906] systemd-udevd[136]: worker [148] terminated by signal 11 (Segmentation fault)
>
> Signed-off-by: Caicai <caizhaopeng@...pin.com>
> ---
>  drivers/gpu/drm/drm_pci.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_pci.c b/drivers/gpu/drm/drm_pci.c
> index 4db9c515b74f..3d1cd760b79c 100644
> --- a/drivers/gpu/drm/drm_pci.c
> +++ b/drivers/gpu/drm/drm_pci.c
> @@ -332,10 +332,12 @@ int drm_pcie_get_speed_cap_mask(struct drm_device *dev, u32 *mask)
>  	u32 lnkcap, lnkcap2;
>  
>  	*mask = 0;
> -	if (!dev->pdev)
> +	if (!dev->pdev || !dev->pdev->bus)
>  		return -EINVAL;
I think we can assume our device is on a bus.
>  	root = dev->pdev->bus->self;
> +	if (!root)
> +		return -EINVAL;
I'm not a PCI expert, but seems like a bad design to say none of the speeds are supported just because we lack a bridge.

btw, drm_pcie_get_max_link_width is similarly affected.

~Maarten

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