Janne Grunau 7254b31a13 media: videobuf2: Set vma_flags in vb2_dma_sg_mmap
vb2_dma_contig sets VMA flags VM_DONTEXPAND and VM_DONTDUMP and I do not
see a reason why vb2_dma_sg should behave differently. This avoids
hitting `WARN_ON(!(vma->vm_flags & VM_DONTEXPAND));` in
drm_gem_mmap_obj() during mmap() of an imported dma-buf from the out of
tree Apple ISP camera capture driver which uses vb2_dma_sg_memops.

gst-launch-1.0 v4l2src ! gtk4paintablesink

[   38.201528] ------------[ cut here ]------------
[   38.202135] WARNING: CPU: 7 PID: 2362 at drivers/gpu/drm/drm_gem.c:1144 drm_gem_mmap_obj+0x1f8/0x210
[   38.203278] Modules linked in: rfcomm snd_seq_dummy snd_hrtimer
snd_seq snd_seq_device uinput nf_conntrack_netbios_ns
nf_conntrack_broadcast nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib
nft_reject_inet nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat
nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables qrtr bnep
nls_ascii i2c_dev loop fuse dm_multipath nfnetlink brcmfmac_wcc
hid_magicmouse hci_bcm4377 brcmfmac brcmutil bluetooth ecdh_generic
cfg80211 ecc btrfs xor xor_neon rfkill hid_apple raid6_pq joydev
aop_als apple_nvmem_spmi industrialio snd_soc_aop apple_z2
snd_soc_cs42l84 tps6598x snd_soc_tas2764 macsmc_reboot spi_nor
macsmc_hwmon rtc_macsmc gpio_macsmc macsmc_power regmap_spmi
macsmc_input dockchannel_hid panel_summit appledrm nvme_apple dwc3
snd_soc_macaudio drm_client_lib nvme_core phy_apple_atc hwmon
apple_sart apple_dockchannel macsmc apple_rtkit_helper
spmi_apple_controller aop apple_wdt mfd_core nvmem_apple_efuses
pinctrl_apple_gpio apple_isp apple_dcp videobuf2_dma_sg mux_core
spi_apple
[   38.203300]  videobuf2_memops i2c_pasemi_platform snd_soc_apple_mca videobuf2_v4l2 videodev clk_apple_nco videobuf2_common snd_pcm_dmaengine adpdrm asahi apple_admac adpdrm_mipi drm_dma_helper pwm_apple i2c_pasemi_core drm_display_helper mc cec apple_dart ofpart apple_soc_cpufreq leds_pwm phram
[   38.217677] CPU: 7 UID: 1000 PID: 2362 Comm: gst-launch-1.0 Tainted: G        W           6.17.6+ #asahi-dev PREEMPT(full)
[   38.219040] Tainted: [W]=WARN
[   38.219398] Hardware name: Apple MacBook Pro (13-inch, M2, 2022) (DT)
[   38.220213] pstate: 21400005 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[   38.221088] pc : drm_gem_mmap_obj+0x1f8/0x210
[   38.221643] lr : drm_gem_mmap_obj+0x78/0x210
[   38.222178] sp : ffffc0008dc678e0
[   38.222579] x29: ffffc0008dc678e0 x28: 0000000000042a97 x27: ffff8000b701b480
[   38.223465] x26: 00000000000000fb x25: ffffc0008dc67d20 x24: ffffc0008dc67968
[   38.224402] x23: ffff8000e3ca5600 x22: ffff8000265b7800 x21: ffff80003000c0c0
[   38.225279] x20: 0000000000000000 x19: ffff8000b68c5200 x18: ffffc0008dc67968
[   38.226151] x17: 0000000000000000 x16: 0000000000000000 x15: ffffc000810a30a8
[   38.227042] x14: 00007fff637effff x13: 00005555de91ffff x12: 00007fff63293fff
[   38.227942] x11: 0000000000000000 x10: ffff8000184ecf08 x9 : ffffc0007a1900c8
[   38.228824] x8 : ffffc0008dc67968 x7 : 0000000000000012 x6 : ffffc0015cf1c000
[   38.229703] x5 : ffffc0008dc676a0 x4 : ffffc00081a27dc0 x3 : 0000000000000038
[   38.230607] x2 : 0000000000000003 x1 : 0000000000000003 x0 : 00000000100000fb
[   38.231488] Call trace:
[   38.231806]  drm_gem_mmap_obj+0x1f8/0x210 (P)
[   38.232342]  drm_gem_mmap+0x140/0x260
[   38.232813]  __mmap_region+0x488/0x9a0
[   38.233277]  mmap_region+0xd0/0x148
[   38.233703]  do_mmap+0x350/0x5c0
[   38.234148]  vm_mmap_pgoff+0x14c/0x200
[   38.234612]  ksys_mmap_pgoff+0x150/0x208
[   38.235107]  __arm64_sys_mmap+0x34/0x50
[   38.235611]  invoke_syscall+0x50/0x120
[   38.236075]  el0_svc_common.constprop.0+0x48/0xf0
[   38.236680]  do_el0_svc+0x24/0x38
[   38.237113]  el0_svc+0x38/0x168
[   38.237507]  el0t_64_sync_handler+0xa0/0xe8
[   38.238034]  el0t_64_sync+0x198/0x1a0
[   38.238491] ---[ end trace 0000000000000000 ]---

There were discussions in [1] at the end of 2023 that mmap() on imported
dma-bufs should not be supported but as of v6.17 drm_gem_shmem_mmap() in
drm_gem_shmem_helper.c still supports it.
This might affect all gpu or accel drivers using drm_gem_shmem_mmap() or
the wrapper drm_gem_shmem_object_mmap().

[1] https://lore.kernel.org/dri-devel/bc7f7844-0aa3-4802-b203-69d58e8be2fa@linux.intel.com/

Cc: stable@vger.kernel.org
Fixes: 5ba3f757f0 ("[media] v4l: videobuf2: add DMA scatter/gather allocator")
Signed-off-by: Janne Grunau <j@jannau.net>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
2026-03-16 11:51:55 +01:00
2026-02-28 15:31:35 +01:00
2026-01-26 19:07:09 -08:00
2026-03-16 11:51:55 +01:00
2025-02-19 14:53:27 -07:00
2026-03-01 15:39:31 -08:00

Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros
* AI Coding Assistant - LLMs and AI-powered development tools


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst
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