niansa-misc/linux
1
0
Fork 0
mirror of synced 2025-03-06 20:59:54 +01:00
Code Issues Projects Releases Packages Wiki Activity
Linux kernel source tree
1327952 commits 2 branches 875 tags 3.5 GiB
C 97.5%
Assembly 1%
Shell 0.6%
Python 0.3%
Makefile 0.3%
Find a file
Frederic Weisbecker 53dac34539 hrtimers: Force migrate away hrtimers queued after CPUHP_AP_HRTIMERS_DYING 
hrtimers are migrated away from the dying CPU to any online target at
the CPUHP_AP_HRTIMERS_DYING stage in order not to delay bandwidth timers
handling tasks involved in the CPU hotplug forward progress.

However wakeups can still be performed by the outgoing CPU after
CPUHP_AP_HRTIMERS_DYING. Those can result again in bandwidth timers being
armed. Depending on several considerations (crystal ball power management
based election, earliest timer already enqueued, timer migration enabled or
not), the target may eventually be the current CPU even if offline. If that
happens, the timer is eventually ignored.

The most notable example is RCU which had to deal with each and every of
those wake-ups by deferring them to an online CPU, along with related
workarounds:

_ e787644caf (rcu: Defer RCU kthreads wakeup when CPU is dying)
_ 9139f93209 (rcu/nocb: Fix RT throttling hrtimer armed from offline CPU)
_ f7345ccc62 (rcu/nocb: Fix rcuog wake-up from offline softirq)

The problem isn't confined to RCU though as the stop machine kthread
(which runs CPUHP_AP_HRTIMERS_DYING) reports its completion at the end
of its work through cpu_stop_signal_done() and performs a wake up that
eventually arms the deadline server timer:

   WARNING: CPU: 94 PID: 588 at kernel/time/hrtimer.c:1086 hrtimer_start_range_ns+0x289/0x2d0
   CPU: 94 UID: 0 PID: 588 Comm: migration/94 Not tainted
   Stopper: multi_cpu_stop+0x0/0x120 <- stop_machine_cpuslocked+0x66/0xc0
   RIP: 0010:hrtimer_start_range_ns+0x289/0x2d0
   Call Trace:
   <TASK>
     start_dl_timer
     enqueue_dl_entity
     dl_server_start
     enqueue_task_fair
     enqueue_task
     ttwu_do_activate
     try_to_wake_up
     complete
     cpu_stopper_thread

Instead of providing yet another bandaid to work around the situation, fix
it in the hrtimers infrastructure instead: always migrate away a timer to
an online target whenever it is enqueued from an offline CPU.

This will also allow to revert all the above RCU disgraceful hacks.

Fixes: 5c0930ccaa ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Reported-by: Vlad Poenaru <vlad.wing@gmail.com>
Reported-by: Usama Arif <usamaarif642@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/all/20250117232433.24027-1-frederic@kernel.org
Closes: 20241213203739.1519801-1-usamaarif642@gmail.com
2025-01-23 20:06:35 +01:00
arch Kthreads affinity follow either of 4 existing different patterns: 2025-01-21 17:10:05 -08:00
block for-6.14/io_uring-20250119 2025-01-20 20:27:33 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto Kthreads affinity follow either of 4 existing different patterns: 2025-01-21 17:10:05 -08:00
Documentation chrome-platform: Updates for v6.14 2025-01-21 19:48:29 -08:00
drivers lsm/stable-6.14 PR 20250121 2025-01-21 20:03:04 -08:00
fs lsm/stable-6.14 PR 20250121 2025-01-21 20:03:04 -08:00
include hrtimers: Force migrate away hrtimers queued after CPUHP_AP_HRTIMERS_DYING 2025-01-23 20:06:35 +01:00
init Rust changes for v6.14 2025-01-21 17:48:03 -08:00
io_uring for-6.14/io_uring-20250119 2025-01-20 20:27:33 -08:00
ipc - The series "resource: A couple of cleanups" from Andy Shevchenko 2024-11-25 16:09:48 -08:00
kernel hrtimers: Force migrate away hrtimers queued after CPUHP_AP_HRTIMERS_DYING 2025-01-23 20:06:35 +01:00
lib Documentation changes this time around include: 2025-01-21 18:00:00 -08:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm Kthreads affinity follow either of 4 existing different patterns: 2025-01-21 17:10:05 -08:00
net lsm/stable-6.14 PR 20250121 2025-01-21 20:03:04 -08:00
rust lsm/stable-6.14 PR 20250121 2025-01-21 20:03:04 -08:00
samples Rust changes for v6.14 2025-01-21 17:48:03 -08:00
scripts Documentation changes this time around include: 2025-01-21 18:00:00 -08:00
security selinux/stable-6.14 PR 20250121 2025-01-21 20:09:14 -08:00
sound drm next for 6.14-rc1 2025-01-21 16:09:47 -08:00
tools lsm/stable-6.14 PR 20250121 2025-01-21 20:03:04 -08:00
usr kbuild: Drop support for include/asm-<arch> in headers_check.pl 2024-12-21 11:43:17 +09:00
virt VFIO updates for v6.13 2024-11-27 12:57:03 -08:00
.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: give Clippy the minimum supported Rust version 2025-01-10 00:17:25 +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 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 rust: use host dylib naming convention to support macOS 2025-01-10 01:01:24 +01:00
.mailmap 7 singleton hotfixes. 6 are MM. 2 are cc:stable and the remainder 2025-01-16 21:24:34 -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 Andy Gospodarek from bonding 2025-01-09 08:30:01 -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 Documentation changes this time around include: 2025-01-21 18:00:00 -08:00
Makefile Rust changes for v6.14 2025-01-21 17:48:03 -08:00
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.