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Linus Torvalds b235848f40 cpumask: limit FORCE_NR_CPUS to just the UP case
[ Upstream commit 5d272dd1b3 ]

Hardcoding the number of CPUs at compile time does improve code
generation, but if you get it wrong the result will be confusion.

We already limited this earlier to only "experts" (see commit
fe5759d5bf "cpumask: limit visibility of FORCE_NR_CPUS"), but with
distro kernel configs often having EXPERT enabled, that turns out to not
be much of a limit.

To quote the philosophers at Disney: "Everyone can be an expert. And
when everyone's an expert, no one will be".

There's a runtime warning if you then set nr_cpus to anything but the
forced number, but apparently that can be ignored too [1] and by then
it's pretty much too late anyway.

If we had some real way to limit this to "embedded only", maybe it would
be worth it, but let's see if anybody even notices that the option is
gone.  We need to simplify kernel configuration anyway.

Link: https://lore.kernel.org/all/20240618105036.208a8860@rorschach.local.home/ [1]
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Paul McKenney <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2024-07-25 09:50:47 +02:00
Documentation scsi: sr: Fix unintentional arithmetic wraparound 2024-07-25 09:50:40 +02:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
arch KVM: PPC: Book3S HV: Prevent UAF in kvm_spapr_tce_attach_iommu_group() 2024-07-25 09:50:47 +02:00
block block/ioctl: prefer different overflow check 2024-06-27 13:49:01 +02:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: aead,cipher - zeroize key buffer after use 2024-07-11 12:49:04 +02:00
drivers spi: Fix OCTAL mode support 2024-07-25 09:50:47 +02:00
fs iomap: Fix iomap_adjust_read_range for plen calculation 2024-07-25 09:50:46 +02:00
include spi: Fix OCTAL mode support 2024-07-25 09:50:47 +02:00
init smp: Provide 'setup_max_cpus' definition on UP too 2024-06-16 13:47:49 +02:00
io_uring io_uring/rsrc: fix incorrect assignment of iter->nr_segs in io_import_fixed 2024-06-27 13:49:10 +02:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel sched: Move psi_account_irqtime() out of update_rq_clock_task() hotpath 2024-07-18 13:21:25 +02:00
lib cpumask: limit FORCE_NR_CPUS to just the UP case 2024-07-25 09:50:47 +02:00
mm mm/damon/core: merge regions aggressively when max_nr_regions is unmet 2024-07-18 13:21:24 +02:00
net wifi: cfg80211: wext: add extra SIOCSIWSCAN data check 2024-07-25 09:50:47 +02:00
rust rust: kernel: require `Send` for `Module` implementations 2024-05-17 12:01:56 +02:00
samples work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:24:47 +01:00
scripts kconfig: remove wrong expr_trans_bool() 2024-07-25 09:50:44 +02:00
security ima: Avoid blocking in RCU read-side critical section 2024-07-11 12:49:18 +02:00
sound ALSA: hda/realtek: Add more codec ID to no shutup pins list 2024-07-25 09:50:47 +02:00
tools selftests/futex: pass _GNU_SOURCE without a value to the compiler 2024-07-25 09:50:43 +02:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-06-27 13:49:11 +02:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rpm-pkg: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +09:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -10:00
.rustfmt.toml rust: add `.rustfmt.toml` 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS pwm: Rename pwm_apply_state() to pwm_apply_might_sleep() 2024-06-12 11:12:24 +02:00
Makefile Linux 6.6.41 2024-07-18 13:21:27 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 Restructured Text 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.