linux-kernel - Re: [PATCH v2 03/16] drm/vkms: Allow to configure multiple planes via configfs

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Message-ID: <fa4f4d3d-6a3e-4659-8a59-4928c2285d55@bootlin.com>
Date: Tue, 4 Mar 2025 16:35:50 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: José Expósito <jose.exposito89@...il.com>
Cc: hamohammed.sa@...il.com, simona@...ll.ch, melissa.srw@...il.com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 airlied@...il.com, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/16] drm/vkms: Allow to configure multiple planes via
 configfs



Le 04/03/2025 à 15:54, José Expósito a écrit :
> Hi Louis,
> 
> On Mon, Mar 03, 2025 at 11:34:50AM +0100, Louis Chauvet wrote:
>>
>>
>> Le 03/03/2025 à 09:50, José Expósito a écrit :
>>> Hi Louis,
>>>
>>> On Fri, Feb 28, 2025 at 03:43:25PM +0100, Louis Chauvet wrote:
>>>>
>>>>
>>>> Le 25/02/2025 à 18:59, José Expósito a écrit :
>>>>> Create a default subgroup at /config/vkms/planes to allow to create as
>>>>> many planes as required.
>>>>>
>>>>> Reviewed-by: Louis Chauvet <louis.chauvet@...tlin.com>
>>>>> Co-developed-by: Louis Chauvet <louis.chauvet@...tlin.com>
>>>>> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
>>>>> Signed-off-by: José Expósito <jose.exposito89@...il.com>
>>>>> [...]
>>>>> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
>>>>> index 92512d52ddae..4f9d3341e6c0 100644
>>>>> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
>>>>> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
>>>>> [...]
>>>>> +static void plane_release(struct config_item *item)
>>>>> +{
>>>>> +	struct vkms_configfs_plane *plane;
>>>>> +	struct mutex *lock;
>>>>> +
>>>>> +	plane = plane_item_to_vkms_configfs_plane(item);
>>>>> +	lock = &plane->dev->lock;
>>>>> +
>>>>> +	guard(mutex)(lock);
>>>>> +	vkms_config_destroy_plane(plane->config);
>>>>> +	kfree(plane);
>>>>> +}
>>>>
>>>> I just found a flaw in our work: there is currently no way to forbid the
>>>> deletion of item/symlinks...
>>>>
>>>> If you do:
>>>>
>>>> modprobe vkms
>>>> cd /sys/kernel/config/vkms/
>>>> mkdir DEV
>>>> mkdir DEV/connectors/CON
>>>> mkdir DEV/planes/PLA
>>>> mkdir DEV/crtcs/CRT
>>>> mkdir DEV/encoders/ENC
>>>> ln -s DEV/crtcs/CRT DEV/planes/PLA/possible_crtcs/
>>>> ln -s DEV/crtcs/CRT DEV/encoders/ENC/possible_crtcs
>>>> ln -s DEV/encoders/ENC DEV/connectors/CON/possible_encoders
>>>> echo 1 > DEV/planes/PLA/type
>>>> tree
>>>> echo 1 > DEV/enabled
>>>> modetest -M vkms
>>>> => everything fine
>>>>
>>>> rm DEV/connectors/CON/possible_encoders/ENC
>>>> rmdir DEV/connectors/CON
>>>> modetest -M vkms
>>>> => BUG: KASAN: slab-use-after-free
> 
> I'm trying to reproduce this issue, but those commands don't show any BUG
> in dmesg. This is my Kasan .config:
> 
>      CONFIG_HAVE_ARCH_KASAN=y
>      CONFIG_HAVE_ARCH_KASAN_VMALLOC=y
>      CONFIG_CC_HAS_KASAN_GENERIC=y
>      CONFIG_CC_HAS_KASAN_SW_TAGS=y
>      CONFIG_CC_HAS_WORKING_NOSANITIZE_ADDRESS=y
>      CONFIG_KASAN=y
>      CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX=y
>      CONFIG_KASAN_GENERIC=y
>      # CONFIG_KASAN_OUTLINE is not set
>      CONFIG_KASAN_INLINE=y
>      CONFIG_KASAN_STACK=y
>      CONFIG_KASAN_VMALLOC=y
>      # CONFIG_KASAN_KUNIT_TEST is not set
>      CONFIG_KASAN_EXTRA_INFO=y
> 
> I tryed to delete even more items:
> 
>      root@...nel-dev:/sys/kernel/config/vkms# tree
>      .
>      └── DEV
>          ├── connectors
>          ├── crtcs
>          ├── enabled
>          ├── encoders
>          └── planes
> 
>      root@...nel-dev:/sys/kernel/config/vkms# cat DEV/enabled
>      1
> 
> And I still don't see any errors. Is it possible that we are running different
> branches? Asking because of the failing IGT tests you reported. There seems to
> be a difference in our code or setup that is creating these differences.

I just re-applied your last vkms-config version and this series on top 
of drm-misc-next. See [1] for the exact commits.

Argg sorry, I just noticed something: you need to disable the default 
vkms device (I had this option in my kernel command line...), otherwise 
modetest only use the first vkms gpu...

I will check again the igt tests, but I don't think this is the same 
issue (it should not use the default device to test)

So, with [1] and the defconfig below, I have this:


     1  modprobe vkms create_default_dev=0
     2  cd /sys/kernel/config/vkms/
     3  mkdir DEV
     4  mkdir DEV/connectors/CON
     5  mkdir DEV/planes/PLA
     6  mkdir DEV/crtcs/CRT
     7  mkdir DEV/encoders/ENC
     8  ln -s DEV/crtcs/CRT DEV/planes/PLA/possible_crtcs/
     9  ln -s DEV/crtcs/CRT DEV/encoders/ENC/possible_crtcs
    10  ln -s DEV/encoders/ENC DEV/connectors/CON/possible_encoders
    11  echo 1 > DEV/planes/PLA/type
    12  tree
    13  echo 1 > DEV/enabled
    14  modetest -M vkms
    15  rm DEV/connectors/CON/possible_encoders/ENC
    16  rmdir DEV/connectors/CON
    17  modetest -M vkms
KASAN: slab-use-after-free


[1]:https://github.com/Fomys/linux/tree/20250225175936.7223-1-jose.exposito89%40gmail.com


===== defconfig =====

CONFIG_SYSVIPC=y
CONFIG_CGROUPS=y
CONFIG_KALLSYMS_ALL=y
CONFIG_SMP=y
CONFIG_HYPERVISOR_GUEST=y
CONFIG_PARAVIRT=y
# CONFIG_VIRTUALIZATION is not set
CONFIG_JUMP_LABEL=y
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
CONFIG_NET=y
CONFIG_PACKET=y
# CONFIG_WIRELESS is not set
CONFIG_NET_9P=y
CONFIG_NET_9P_VIRTIO=y
CONFIG_PCI=y
CONFIG_DEVTMPFS=y
CONFIG_DEVTMPFS_MOUNT=y
CONFIG_VIRTIO_BLK=y
# CONFIG_INTEL_MEI is not set
CONFIG_NETDEVICES=y
CONFIG_VIRTIO_NET=y
# CONFIG_ETHERNET is not set
# CONFIG_WLAN is not set
CONFIG_INPUT_EVDEV=y
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_VIRTIO_CONSOLE=y
CONFIG_HW_RANDOM_VIRTIO=m
CONFIG_PTP_1588_CLOCK=y
# CONFIG_HWMON is not set
CONFIG_THERMAL_GOV_USER_SPACE=y
CONFIG_DRM=y
CONFIG_DRM_KUNIT_TEST=m
CONFIG_DRM_VKMS=m
CONFIG_DRM_VKMS_KUNIT_TEST=m
# CONFIG_USB_SUPPORT is not set
CONFIG_VIRTIO_PCI=y
CONFIG_VIRTIO_BALLOON=y
CONFIG_VIRTIO_INPUT=y
CONFIG_VIRTIO_MMIO=y
CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES=y
# CONFIG_SURFACE_PLATFORMS is not set
CONFIG_EXT4_FS=y
CONFIG_FUSE_FS=y
CONFIG_VIRTIO_FS=y
CONFIG_OVERLAY_FS=y
CONFIG_TMPFS=y
CONFIG_TMPFS_POSIX_ACL=y
CONFIG_CONFIGFS_FS=y
CONFIG_9P_FS=y
CONFIG_CRYPTO=y
CONFIG_CRYPTO_CRC32C=y
CONFIG_DYNAMIC_DEBUG=y
CONFIG_DEBUG_KERNEL=y
CONFIG_DEBUG_INFO_DWARF5=y
CONFIG_MAGIC_SYSRQ=y
CONFIG_DEBUG_FS=y
CONFIG_DEBUG_PAGEALLOC=y
CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y
CONFIG_PAGE_POISONING=y
CONFIG_DEBUG_OBJECTS=y
CONFIG_DEBUG_OBJECTS_RCU_HEAD=y
CONFIG_SCHED_STACK_END_CHECK=y
CONFIG_KASAN=y
CONFIG_KASAN_VMALLOC=y
CONFIG_KASAN_EXTRA_INFO=y
CONFIG_KFENCE=y
# CONFIG_FTRACE is not set
CONFIG_UNWINDER_FRAME_POINTER=y
CONFIG_KUNIT=y
CONFIG_TEST_DYNAMIC_DEBUG=m