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Remi Pommarel c2ddf2f576 leds: Fix LED_OFF brightness race 
[ Upstream commit 2c70953b6f ]

While commit fa15d8c692 ("leds: Fix set_brightness_delayed() race")
successfully forces led_set_brightness() to be called with LED_OFF at
least once when switching from blinking to LED on state so that
hw-blinking can be disabled, another race remains. Indeed in
led_set_brightness(LED_OFF) followed by led_set_brightness(any)
scenario the following CPU scheduling can happen:

    CPU0                                     CPU1
    ----                                     ----
 set_brightness_delayed() {
   test_and_clear_bit(BRIGHTNESS_OFF)
                                         led_set_brightness(LED_OFF) {
                                           set_bit(BRIGHTNESS_OFF)
					   queue_work()
                                         }
                                         led_set_brightness(any) {
                                           set_bit(BRIGHTNESS)
					   queue_work() //already queued
                                         }
   test_and_clear_bit(BRIGHTNESS)
     /* LED set with brightness any */
 }

 /* From previous CPU1 queue_work() */
 set_brightness_delayed() {
   test_and_clear_bit(BRIGHTNESS_OFF)
     /* LED turned off */
   test_and_clear_bit(BRIGHTNESS)
     /* Clear from previous run, LED remains off */

In that case the led_set_brightness(LED_OFF)/led_set_brightness(any)
sequence will be effectively executed in reverse order and LED will
remain off.

With the introduction of commit 32360bf6a5 ("leds: Introduce ordered
workqueue for LEDs events instead of system_wq") the race is easier to
trigger as sysfs brightness configuration does not wait for
set_brightness_delayed() work to finish (flush_work() removal).

Use delayed_set_value to optionnally re-configure brightness after a
LED_OFF. That way a LED state could be configured more that once but
final state will always be as expected. Ensure that delayed_set_value
modification is seen before set_bit() using smp_mb__before_atomic().

Fixes: fa15d8c692 ("leds: Fix set_brightness_delayed() race")
Signed-off-by: Remi Pommarel <repk@triplefau.lt>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/19c81177059dab7b656c42063958011a8e4d1a66.1740050412.git.repk@triplefau.lt
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-04-10 14:39:21 +02:00
arch x86/entry: Fix ORC unwinder for PUSH_REGS with save_ret=1 2025-04-10 14:39:20 +02:00
block block: fix 'kmem_cache of name 'bio-108' already exists' 2025-03-22 12:54:21 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: api - Fix larval relookup type and mask 2025-04-10 14:39:20 +02:00
Documentation dt-bindings: vendor-prefixes: add GOcontroll 2025-04-10 14:39:13 +02:00
drivers leds: Fix LED_OFF brightness race 2025-04-10 14:39:21 +02:00
fs bcachefs: bch2_ioctl_subvolume_destroy() fixes 2025-04-07 10:08:37 +02:00
include RDMA/core: Don't expose hw_counters outside of init net namespace 2025-04-10 14:39:19 +02:00
init rust: Disallow BTF generation with Rust + LTO 2025-03-22 12:54:23 -07:00
io_uring io_uring/net: fix sendzc double notif flush 2025-03-28 22:03:32 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel bpf: Fix array bounds error with may_goto 2025-04-10 14:39:21 +02:00
lib rust: fix signature of rust_fmt_argument 2025-04-10 14:39:20 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range() 2025-04-10 14:39:18 +02:00
net netfilter: socket: Lookup orig tuple for IPv6 SNAT 2025-04-07 10:08:35 +02:00
rust rust: fix signature of rust_fmt_argument 2025-04-10 14:39:20 +02:00
samples rust: treewide: switch to the kernel Vec type 2025-03-13 13:01:46 +01:00
scripts selinux: Chain up tool resolving errors in install_policy.sh 2025-04-10 14:39:11 +02:00
security smack: ipv4/ipv6: tcp/dccp/sctp: fix incorrect child socket label 2025-04-10 14:39:10 +02:00
sound ALSA: timer: Don't take register_mutex with copy_from/to_user() 2025-04-10 14:39:13 +02:00
tools selftests/bpf: Select NUMA_NO_NODE to create map 2025-04-10 14:39:20 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: x86: switch hugepage recovery thread to vhost_task 2024-12-05 14:02:43 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: enable Clippy's check-private-items 2025-03-13 13:01:42 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.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 MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
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 MAINTAINERS: add entry for the Rust alloc module 2025-03-13 13:01:47 +01:00
Makefile Linux 6.12.22 2025-04-07 10:08:37 +02:00
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.