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Tue, 04 Mar 2025 08:24:01 -0800 (PST) Date: Tue, 4 Mar 2025 17:23:59 +0100 From: =?iso-8859-1?Q?Jos=E9_Exp=F3sito?= To: Louis Chauvet Cc: hamohammed.sa@gmail.com, simona@ffwll.ch, melissa.srw@gmail.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 03/16] drm/vkms: Allow to configure multiple planes via configfs Message-ID: References: <20250225175936.7223-1-jose.exposito89@gmail.com> <20250225175936.7223-4-jose.exposito89@gmail.com> <52bc3f15-28da-4b40-917f-981f1f10d9b8@bootlin.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Mar 04, 2025 at 04:35:50PM +0100, Louis Chauvet wrote: > > > 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 > > > > > > Co-developed-by: Louis Chauvet > > > > > > Signed-off-by: Louis Chauvet > > > > > > Signed-off-by: José Expósito > > > > > > [...] > > > > > > 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@kernel-dev:/sys/kernel/config/vkms# tree > > . > > └── DEV > > ├── connectors > > ├── crtcs > > ├── enabled > > ├── encoders > > └── planes > > > > root@kernel-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 Aha! Are you testing without a desktop environment running? $ sudo systemctl isolate multi-user.target Running that (^) command before yours gives me this use after free: BUG: KASAN: slab-use-after-free in vkms_connector_detect+0x61/0x70 [vkms] Is the same one you are seeing? Looking at the connector_release() function in vkms_configfs.c, I see that I'm freeing the configuration: vkms_config_destroy_connector(connector->config); And I don't think there is a reason to do it. vkms_config_destroy() in device_release() will free everything once we are done. I need to do more testing, but the solution might be that simple. Good catch, I didn't test like that and I overlooked this issue :D Jose > > > ===== 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 >