linux/Documentation/core-api/kernel-api.rst, branch v6.4

module: add debug stats to help identify memory pressure

2023-04-18T18:15:24Z

Loading modules with finit_module() can end up using vmalloc(), vmap() and vmalloc() again, for a total of up to 3 separate allocations in the worst case for a single module. We always kernel_read*() the module, that's a vmalloc(). Then vmap() is used for the module decompression, and if so the last read buffer is freed as we use the now decompressed module buffer to stuff data into our copy module. The last allocation is specific to each architectures but pretty much that's generally a series of vmalloc() calls or a variation of vmalloc to handle ELF sections with special permissions. Evaluation with new stress-ng module support [1] with just 100 ops is proving that you can end up using GiBs of data easily even with all care we have in the kernel and userspace today in trying to not load modules which are already loaded. 100 ops seems to resemble the sort of pressure a system with about 400 CPUs can create on module loading. Although issues relating to duplicate module requests due to each CPU inucurring a new module reuest is silly and some of these are being fixed, we currently lack proper tooling to help diagnose easily what happened, when it happened and who likely is to blame -- userspace or kernel module autoloading. Provide an initial set of stats which use debugfs to let us easily scrape post-boot information about failed loads. This sort of information can be used on production worklaods to try to optimize *avoiding* redundant memory pressure using finit_module(). There's a few examples that can be provided: A 255 vCPU system without the next patch in this series applied: Startup finished in 19.143s (kernel) + 7.078s (userspace) = 26.221s graphical.target reached after 6.988s in userspace And 13.58 GiB of virtual memory space lost due to failed module loading: root@big ~ # cat /sys/kernel/debug/modules/stats Mods ever loaded 67 Mods failed on kread 0 Mods failed on decompress 0 Mods failed on becoming 0 Mods failed on load 1411 Total module size 11464704 Total mod text size 4194304 Failed kread bytes 0 Failed decompress bytes 0 Failed becoming bytes 0 Failed kmod bytes 14588526272 Virtual mem wasted bytes 14588526272 Average mod size 171115 Average mod text size 62602 Average fail load bytes 10339140 Duplicate failed modules: module-name How-many-times Reason kvm_intel 249 Load kvm 249 Load irqbypass 8 Load crct10dif_pclmul 128 Load ghash_clmulni_intel 27 Load sha512_ssse3 50 Load sha512_generic 200 Load aesni_intel 249 Load crypto_simd 41 Load cryptd 131 Load evdev 2 Load serio_raw 1 Load virtio_pci 3 Load nvme 3 Load nvme_core 3 Load virtio_pci_legacy_dev 3 Load virtio_pci_modern_dev 3 Load t10_pi 3 Load virtio 3 Load crc32_pclmul 6 Load crc64_rocksoft 3 Load crc32c_intel 40 Load virtio_ring 3 Load crc64 3 Load The following screen shot, of a simple 8vcpu 8 GiB KVM guest with the next patch in this series applied, shows 226.53 MiB are wasted in virtual memory allocations which due to duplicate module requests during boot. It also shows an average module memory size of 167.10 KiB and an an average module .text + .init.text size of 61.13 KiB. The end shows all modules which were detected as duplicate requests and whether or not they failed early after just the first kernel_read*() call or late after we've already allocated the private space for the module in layout_and_allocate(). A system with module decompression would reveal more wasted virtual memory space. We should put effort now into identifying the source of these duplicate module requests and trimming these down as much possible. Larger systems will obviously show much more wasted virtual memory allocations. root@kmod ~ # cat /sys/kernel/debug/modules/stats Mods ever loaded 67 Mods failed on kread 0 Mods failed on decompress 0 Mods failed on becoming 83 Mods failed on load 16 Total module size 11464704 Total mod text size 4194304 Failed kread bytes 0 Failed decompress bytes 0 Failed becoming bytes 228959096 Failed kmod bytes 8578080 Virtual mem wasted bytes 237537176 Average mod size 171115 Average mod text size 62602 Avg fail becoming bytes 2758544 Average fail load bytes 536130 Duplicate failed modules: module-name How-many-times Reason kvm_intel 7 Becoming kvm 7 Becoming irqbypass 6 Becoming & Load crct10dif_pclmul 7 Becoming & Load ghash_clmulni_intel 7 Becoming & Load sha512_ssse3 6 Becoming & Load sha512_generic 7 Becoming & Load aesni_intel 7 Becoming crypto_simd 7 Becoming & Load cryptd 3 Becoming & Load evdev 1 Becoming serio_raw 1 Becoming nvme 3 Becoming nvme_core 3 Becoming t10_pi 3 Becoming virtio_pci 3 Becoming crc32_pclmul 6 Becoming & Load crc64_rocksoft 3 Becoming crc32c_intel 3 Becoming virtio_pci_modern_dev 2 Becoming virtio_pci_legacy_dev 1 Becoming crc64 2 Becoming virtio 2 Becoming virtio_ring 2 Becoming [0] https://github.com/ColinIanKing/stress-ng.git [1] echo 0 > /proc/sys/vm/oom_dump_tasks ./stress-ng --module 100 --module-name xfs Signed-off-by: Luis Chamberlain

Documentation: core-api: update kernel-doc reference to kmod.c

2023-03-24T18:33:09Z

Commit d6f819908f8aac ("module: fold usermode helper kmod into modules directory") moves kmod helper implementation (kmod.c) to kernel/module/ directory but forgets to update its reference on kernel api doc, hence: WARNING: kernel-doc './scripts/kernel-doc -rst -enable-lineno -sphinx-version 2.4.4 -export ./kernel/kmod.c' failed with return code 2 Update the reference. Fixes: d6f819908f8aac ("module: fold usermode helper kmod into modules directory") Reported-by: Stephen Rothwell Link: https://lore.kernel.org/linux-next/20230324154413.19cc78be@canb.auug.org.au/ Signed-off-by: Bagas Sanjaya Reviewed-by: Liam Beguin Signed-off-by: Luis Chamberlain

Merge tag 'hardening-v6.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

2022-12-14T20:20:00Z

Pull kernel hardening updates from Kees Cook: - Convert flexible array members, fix -Wstringop-overflow warnings, and fix KCFI function type mismatches that went ignored by maintainers (Gustavo A. R. Silva, Nathan Chancellor, Kees Cook) - Remove the remaining side-effect users of ksize() by converting dma-buf, btrfs, and coredump to using kmalloc_size_roundup(), add more __alloc_size attributes, and introduce full testing of all allocator functions. Finally remove the ksize() side-effect so that each allocation-aware checker can finally behave without exceptions - Introduce oops_limit (default 10,000) and warn_limit (default off) to provide greater granularity of control for panic_on_oops and panic_on_warn (Jann Horn, Kees Cook) - Introduce overflows_type() and castable_to_type() helpers for cleaner overflow checking - Improve code generation for strscpy() and update str*() kern-doc - Convert strscpy and sigphash tests to KUnit, and expand memcpy tests - Always use a non-NULL argument for prepare_kernel_cred() - Disable structleak plugin in FORTIFY KUnit test (Anders Roxell) - Adjust orphan linker section checking to respect CONFIG_WERROR (Xin Li) - Make sure siginfo is cleared for forced SIGKILL (haifeng.xu) - Fix um vs FORTIFY warnings for always-NULL arguments * tag 'hardening-v6.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: (31 commits) ksmbd: replace one-element arrays with flexible-array members hpet: Replace one-element array with flexible-array member um: virt-pci: Avoid GCC non-NULL warning signal: Initialize the info in ksignal lib: fortify_kunit: build without structleak plugin panic: Expose "warn_count" to sysfs panic: Introduce warn_limit panic: Consolidate open-coded panic_on_warn checks exit: Allow oops_limit to be disabled exit: Expose "oops_count" to sysfs exit: Put an upper limit on how often we can oops panic: Separate sysctl logic from CONFIG_SMP mm/pgtable: Fix multiple -Wstringop-overflow warnings mm: Make ksize() a reporting-only function kunit/fortify: Validate __alloc_size attribute results drm/sti: Fix return type of sti_{dvo,hda,hdmi}_connector_mode_valid() drm/fsl-dcu: Fix return type of fsl_dcu_drm_connector_mode_valid() driver core: Add __alloc_size hint to devm allocators overflow: Introduce overflows_type() and castable_to_type() coredump: Proactively round up to kmalloc bucket size ...

Merge tag 'docs-6.2' of git://git.lwn.net/linux

2022-12-13T01:18:50Z

Pull documentation updates from Jonathan Corbet: "This was a not-too-busy cycle for documentation; highlights include: - The beginnings of a set of translations into Spanish, headed up by Carlos Bilbao - More Chinese translations - A change to the Sphinx "alabaster" theme by default for HTML generation. Unlike the previous default (Read the Docs), alabaster is shipped with Sphinx by default, reducing the number of other dependencies that need to be installed. It also (IMO) produces a cleaner and more readable result. - The ability to render the documentation into the texinfo format (something Sphinx could always do, we just never wired it up until now) Plus the usual collection of typo fixes, build-warning fixes, and minor updates" * tag 'docs-6.2' of git://git.lwn.net/linux: (67 commits) Documentation/features: Use loongarch instead of loong Documentation/features-refresh.sh: Only sed the beginning "arch" of ARCH_DIR docs/zh_CN: Fix '.. only::' directive's expression docs/sp_SP: Add memory-barriers.txt Spanish translation docs/zh_CN/LoongArch: Update links of LoongArch ISA Vol1 and ELF psABI docs/LoongArch: Update links of LoongArch ISA Vol1 and ELF psABI Documentation/features: Update feature lists for 6.1 Documentation: Fixed a typo in bootconfig.rst docs/sp_SP: Add process coding-style translation docs/sp_SP: Add kernel-docs.rst Spanish translation docs: Create translations/sp_SP/process/, move submitting-patches.rst docs: Add book to process/kernel-docs.rst docs: Retire old resources from kernel-docs.rst docs: Update maintainer of kernel-docs.rst Documentation: riscv: Document the sv57 VM layout Documentation: USB: correct possessive "its" usage math64: fix kernel-doc return value warnings math64: add kernel-doc for DIV64_U64_ROUND_UP math64: favor kernel-doc from header files doc: add texinfodocs and infodocs targets ...

math64: favor kernel-doc from header files

2022-11-21T21:30:53Z

Fix the kernel-doc markings for div64 functions to point to the header file instead of the lib/ directory. This avoids having implementation specific comments in generic documentation. Furthermore, given that some kernel-doc comments are identical, drop them from lib/math64 and only keep there comments that add implementation details. Signed-off-by: Liam Beguin Acked-by: Randy Dunlap Tested-by: Randy Dunlap Link: https://lore.kernel.org/r/20221118182309.3824530-1-liambeguin@gmail.com Signed-off-by: Jonathan Corbet

string: Rewrite and add more kern-doc for the str*() functions

2022-10-28T23:07:57Z

While there were varying degrees of kern-doc for various str*()-family functions, many needed updating and clarification, or to just be entirely written. Update (and relocate) existing kern-doc and add missing functions, sadly shaking my head at how many times I have written "Do not use this function". Include the results in the core kernel API doc. Cc: Bagas Sanjaya Cc: Andy Shevchenko Cc: Rasmus Villemoes Cc: Andrew Morton Cc: linux-hardening@vger.kernel.org Tested-by: Akira Yokosawa Link: https://lore.kernel.org/lkml/9b0cf584-01b3-3013-b800-1ef59fe82476@gmail.com Signed-off-by: Kees Cook

overflow: Fix kern-doc markup for functions

2022-10-25T21:57:42Z

Fix the kern-doc markings for several of the overflow helpers and move their location into the core kernel API documentation, where it belongs (it's not driver-specific). Cc: Jonathan Corbet Cc: linux-doc@vger.kernel.org Cc: linux-hardening@vger.kernel.org Reviewed-by: Akira Yokosawa Signed-off-by: Kees Cook

doc: module: update file references

2022-07-01T21:50:01Z

Adjust documents to the file moves made by commit cfc1d277891e ("module: Move all into module/"). Thanks to Yanteng Si for helping me to update Documentation/translations/zh_CN/core-api/kernel-api.rst Signed-off-by: Masahiro Yamada Acked-by: Yanteng Si Signed-off-by: Luis Chamberlain

Merge tag 'iomap-5.17' of git://git.infradead.org/users/willy/linux

2022-01-12T20:51:41Z

Pull iomap updates from Matthew Wilcox: "Convert xfs/iomap to use folios. This should be all that is needed for XFS to use large folios. There is no code in this pull request to create large folios, but no additional changes should be needed to XFS or iomap once they are created. Usually this would have come from Darrick, and we had intended that it would come that route. Between the holidays and various things which Darrick needed to work on, he asked if I could send things directly. There weren't any other iomap patches pending for this release, which probably also played a role" * tag 'iomap-5.17' of git://git.infradead.org/users/willy/linux: (26 commits) iomap: Inline __iomap_zero_iter into its caller xfs: Support large folios iomap: Support large folios in invalidatepage iomap: Convert iomap_migrate_page() to use folios iomap: Convert iomap_add_to_ioend() to take a folio iomap: Simplify iomap_do_writepage() iomap: Simplify iomap_writepage_map() iomap,xfs: Convert ->discard_page to ->discard_folio iomap: Convert iomap_write_end_inline to take a folio iomap: Convert iomap_write_begin() and iomap_write_end() to folios iomap: Convert __iomap_zero_iter to use a folio iomap: Allow iomap_write_begin() to be called with the full length iomap: Convert iomap_page_mkwrite to use a folio iomap: Convert readahead and readpage to use a folio iomap: Convert iomap_read_inline_data to take a folio iomap: Use folio offsets instead of page offsets iomap: Convert bio completions to use folios iomap: Pass the iomap_page into iomap_set_range_uptodate iomap: Add iomap_invalidate_folio iomap: Convert iomap_releasepage to use a folio ...

block: Add bio_for_each_folio_all()

2021-12-16T20:49:51Z

Allow callers to iterate over each folio instead of each page. The bio need not have been constructed using folios originally. Signed-off-by: Matthew Wilcox (Oracle) Reviewed-by: Jens Axboe Reviewed-by: Christoph Hellwig Reviewed-by: Darrick J. Wong