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Vlastimil Babka 82efd569a8 locking/local_lock: fix _Generic() matching of local_trylock_t 
Michael Larabel reported [1] a nginx performance regression in v6.15-rc3
and bisected it to commit 51339d99c0 ("locking/local_lock, mm: replace
localtry_ helpers with local_trylock_t type")

The problem is the _Generic() usage with a default association that
masks the fact that "local_trylock_t *" association is not being
selected as expected.  Replacing the default with the only other
expected type "local_lock_t *" reveals the underlying problem:

  include/linux/local_lock_internal.h:174:26: error: ‘_Generic’ selector of type ‘__seg_gs local_lock_t *’ is not compatible with any association

The local_locki's are part of __percpu structures and thus the __percpu
attribute is needed to associate the type properly.  Add the attribute
and keep the default replaced to turn any further mismatches into
compile errors.

The failure to recognize local_try_lock_t in __local_lock_release()
means that a local_trylock[_irqsave]() operation will set tl->acquired
to 1 (there's no _Generic() part in the trylock code), but then
local_unlock[_irqrestore]() will not set tl->acquired back to 0, so
further trylock operations will always fail on the same cpu+lock, while
non-trylock operations continue to work - a lockdep_assert() is also not
being executed in the _Generic() part of local_lock() code.

This means consume_stock() and refill_stock() operations will fail
deterministically, resulting in taking the slow paths and worse
performance.

Fixes: 51339d99c0 ("locking/local_lock, mm: replace localtry_ helpers with local_trylock_t type")
Reported-by: Michael Larabel <Michael@phoronix.com>
Closes: https://www.phoronix.com/review/linux-615-nginx-regression/2 [1]
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-04-23 09:04:56 -07:00
arch Miscellaneous x86 fixes: 2025-04-18 14:04:57 -07:00
block vfs-6.15-rc3.fixes.2 2025-04-19 14:31:08 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: ahash - Disable request chaining 2025-04-12 09:33:09 +08:00
Documentation 16 hotfixes. 2 are cc:stable and the remainder address post-6.14 issues 2025-04-19 21:46:58 -07:00
drivers virtio, vhost: fixes 2025-04-23 08:25:56 -07:00
fs for-6.15-rc3-tag 2025-04-22 10:22:38 -07:00
include locking/local_lock: fix _Generic() matching of local_trylock_t 2025-04-23 09:04:56 -07:00
init Kconfig: switch CONFIG_SYSFS_SYCALL default to n 2025-04-15 10:28:35 +02:00
io_uring io_uring/zcrx: fix late dma unmap for a dead dev 2025-04-18 06:12:10 -06:00
ipc treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
kernel virtio, vhost: fixes 2025-04-23 08:25:56 -07:00
lib hardening fixes for v6.15-rc3 2025-04-18 13:20:20 -07:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm 16 hotfixes. 2 are cc:stable and the remainder address post-6.14 issues 2025-04-19 21:46:58 -07:00
net Including fixes from Bluetooth, CAN and Netfilter. 2025-04-17 11:45:30 -07:00
rust rust: helpers: Add dma_alloc_attrs() and dma_free_attrs() 2025-04-15 23:06:03 +02:00
samples samples/livepatch: add module descriptions 2025-04-11 17:32:38 -07:00
scripts Rust fixes for v6.15 2025-04-19 10:02:43 -07:00
security ima: process_measurement() needlessly takes inode_lock() on MAY_READ 2025-04-22 16:39:32 +02:00
sound ASoC: Fixes for v6.15 2025-04-11 15:51:19 +02:00
tools sched_ext: Fixes for v6.15-rc3 2025-04-21 19:16:29 -07:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-05 04:06:45 +09:00
virt ARM: 2025-04-08 13:47:55 -07:00
.clang-format clang-format: Update the ForEachMacros list for v6.15-rc1 2025-04-13 11:03:59 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-01-10 00:17:25 +01:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: Create intermediate vmlinux build with relocations preserved 2025-03-17 00:29:50 +09:00
.mailmap sound fixes for 6.15-rc3 2025-04-17 10:14:51 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING
CREDITS MAINTAINERS: update SLAB ALLOCATOR maintainers 2025-04-17 20:10:06 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS 16 hotfixes. 2 are cc:stable and the remainder address post-6.14 issues 2025-04-19 21:46:58 -07:00
Makefile gcc-15: disable '-Wunterminated-string-initialization' entirely for now 2025-04-20 15:30:53 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.