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Colin Ian King 2de76cf01e x86/lib: Fix overflow when counting digits 
[ Upstream commit a24d61c609 ]

tl;dr: The num_digits() function has a theoretical overflow issue.
But it doesn't affect any actual in-tree users.  Fix it by using
a larger type for one of the local variables.

Long version:

There is an overflow in variable m in function num_digits when val
is >= 1410065408 which leads to the digit calculation loop to
iterate more times than required. This results in either more
digits being counted or in some cases (for example where val is
1932683193) the value of m eventually overflows to zero and the
while loop spins forever).

Currently the function num_digits is currently only being used for
small values of val in the SMP boot stage for digit counting on the
number of cpus and NUMA nodes, so the overflow is never encountered.
However it is useful to fix the overflow issue in case the function
is used for other purposes in the future. (The issue was discovered
while investigating the digit counting performance in various
kernel helper functions rather than any real-world use-case).

The simplest fix is to make m a long long, the overhead in
multiplication speed for a long long is very minor for small values
of val less than 10000 on modern processors. The alternative
fix is to replace the multiplication with a constant division
by 10 loop (this compiles down to an multiplication and shift)
without needing to make m a long long, but this is slightly slower
than the fix in this commit when measured on a range of x86
processors).

[ dhansen: subject and changelog tweaks ]

Fixes: 646e29a178 ("x86: Improve the printout of the SMP bootup CPU table")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20231102174901.2590325-1-colin.i.king%40gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
2024-01-25 15:35:12 -08:00
arch x86/lib: Fix overflow when counting digits 2024-01-25 15:35:12 -08:00
block blk-mq: don't count completed flush data request as inflight in case of quiesce 2024-01-20 11:51:39 +01:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: xts - use 'spawn' for underlying single-block cipher 2024-01-10 17:16:54 +01:00
Documentation dt-bindings: nvmem: mxs-ocotp: Document fsl,ocotp 2024-01-01 12:42:42 +00:00
drivers coresight: etm4x: Fix width of CCITMIN field 2024-01-20 11:51:49 +01:00
fs ksmbd: free ppace array on error in parse_dacl 2024-01-20 11:51:48 +01:00
include driver core: Add a guard() definition for the device_lock() 2024-01-20 11:51:44 +01:00
init proc: sysctl: prevent aliased sysctls from getting passed to init 2023-11-28 17:19:57 +00:00
io_uring io_uring: use fget/fput consistently 2024-01-20 11:51:38 +01:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel posix-timers: Get rid of [COMPAT_]SYS_NI() uses 2024-01-20 11:51:46 +01:00
lib ida: Fix crash in ida_free when the bitmap is empty 2024-01-20 11:51:46 +01:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/memory_hotplug: fix memmap_on_memory sysfs value retrieval 2024-01-20 11:51:49 +01:00
net net: qrtr: ns: Return 0 if server port is not present 2024-01-20 11:51:47 +01:00
rust rust: docs: fix logo replacement 2023-10-19 16:40:00 +02:00
samples vfio/mtty: Overhaul mtty interrupt handling 2024-01-10 17:16:55 +01:00
scripts scripts/decode_stacktrace.sh: optionally use LLVM utilities 2024-01-20 11:51:49 +01:00
security apparmor: Fix move_mount mediation by detecting if source is detached 2024-01-10 17:16:52 +01:00
sound ASoC: SOF: Intel: hda-codec: Delay the codec device registration 2024-01-20 11:51:47 +01:00
tools kselftest: alsa: fixed a print formatting warning 2024-01-20 11:51:45 +01:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt ARM: 2023-09-07 13:52:20 -07:00
.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
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
MAINTAINERS Char/Misc driver fixes for 6.6-final 2023-10-28 07:51:27 -10:00
Makefile Linux 6.6.13 2024-01-20 11:51:49 +01:00
README

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.